448 lines
13 KiB
C
448 lines
13 KiB
C
/*
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* FP/SIMD context switching and fault handling
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*
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* Copyright (C) 2012 ARM Ltd.
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* Author: Catalin Marinas <catalin.marinas@arm.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/bottom_half.h>
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#include <linux/cpu.h>
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#include <linux/cpu_pm.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/percpu.h>
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#include <linux/preempt.h>
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#include <linux/sched/signal.h>
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#include <linux/signal.h>
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#include <asm/fpsimd.h>
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#include <asm/cputype.h>
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#include <asm/simd.h>
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#define FPEXC_IOF (1 << 0)
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#define FPEXC_DZF (1 << 1)
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#define FPEXC_OFF (1 << 2)
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#define FPEXC_UFF (1 << 3)
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#define FPEXC_IXF (1 << 4)
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#define FPEXC_IDF (1 << 7)
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/*
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* In order to reduce the number of times the FPSIMD state is needlessly saved
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* and restored, we need to keep track of two things:
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* (a) for each task, we need to remember which CPU was the last one to have
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* the task's FPSIMD state loaded into its FPSIMD registers;
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* (b) for each CPU, we need to remember which task's userland FPSIMD state has
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* been loaded into its FPSIMD registers most recently, or whether it has
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* been used to perform kernel mode NEON in the meantime.
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*
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* For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
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* the id of the current CPU every time the state is loaded onto a CPU. For (b),
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* we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
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* address of the userland FPSIMD state of the task that was loaded onto the CPU
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* the most recently, or NULL if kernel mode NEON has been performed after that.
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*
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* With this in place, we no longer have to restore the next FPSIMD state right
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* when switching between tasks. Instead, we can defer this check to userland
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* resume, at which time we verify whether the CPU's fpsimd_last_state and the
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* task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
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* can omit the FPSIMD restore.
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*
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* As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
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* indicate whether or not the userland FPSIMD state of the current task is
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* present in the registers. The flag is set unless the FPSIMD registers of this
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* CPU currently contain the most recent userland FPSIMD state of the current
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* task.
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*
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* In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may
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* save the task's FPSIMD context back to task_struct from softirq context.
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* To prevent this from racing with the manipulation of the task's FPSIMD state
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* from task context and thereby corrupting the state, it is necessary to
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* protect any manipulation of a task's fpsimd_state or TIF_FOREIGN_FPSTATE
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* flag with local_bh_disable() unless softirqs are already masked.
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*
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* For a certain task, the sequence may look something like this:
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* - the task gets scheduled in; if both the task's fpsimd_state.cpu field
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* contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
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* variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
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* cleared, otherwise it is set;
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*
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* - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
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* userland FPSIMD state is copied from memory to the registers, the task's
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* fpsimd_state.cpu field is set to the id of the current CPU, the current
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* CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
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* TIF_FOREIGN_FPSTATE flag is cleared;
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*
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* - the task executes an ordinary syscall; upon return to userland, the
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* TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
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* restored;
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*
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* - the task executes a syscall which executes some NEON instructions; this is
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* preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
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* register contents to memory, clears the fpsimd_last_state per-cpu variable
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* and sets the TIF_FOREIGN_FPSTATE flag;
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*
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* - the task gets preempted after kernel_neon_end() is called; as we have not
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* returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
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* whatever is in the FPSIMD registers is not saved to memory, but discarded.
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*/
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static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
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/*
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* Trapped FP/ASIMD access.
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*/
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void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
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{
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/* TODO: implement lazy context saving/restoring */
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WARN_ON(1);
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}
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/*
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* Raise a SIGFPE for the current process.
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*/
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void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
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{
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siginfo_t info;
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unsigned int si_code = 0;
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if (esr & FPEXC_IOF)
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si_code = FPE_FLTINV;
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else if (esr & FPEXC_DZF)
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si_code = FPE_FLTDIV;
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else if (esr & FPEXC_OFF)
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si_code = FPE_FLTOVF;
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else if (esr & FPEXC_UFF)
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si_code = FPE_FLTUND;
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else if (esr & FPEXC_IXF)
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si_code = FPE_FLTRES;
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memset(&info, 0, sizeof(info));
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info.si_signo = SIGFPE;
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info.si_code = si_code;
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info.si_addr = (void __user *)instruction_pointer(regs);
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send_sig_info(SIGFPE, &info, current);
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}
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void fpsimd_thread_switch(struct task_struct *next)
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{
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if (!system_supports_fpsimd())
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return;
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/*
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* Save the current FPSIMD state to memory, but only if whatever is in
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* the registers is in fact the most recent userland FPSIMD state of
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* 'current'.
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*/
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if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
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fpsimd_save_state(¤t->thread.fpsimd_state);
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if (next->mm) {
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/*
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* If we are switching to a task whose most recent userland
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* FPSIMD state is already in the registers of *this* cpu,
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* we can skip loading the state from memory. Otherwise, set
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* the TIF_FOREIGN_FPSTATE flag so the state will be loaded
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* upon the next return to userland.
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*/
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struct fpsimd_state *st = &next->thread.fpsimd_state;
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if (__this_cpu_read(fpsimd_last_state) == st
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&& st->cpu == smp_processor_id())
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clear_ti_thread_flag(task_thread_info(next),
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TIF_FOREIGN_FPSTATE);
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else
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set_ti_thread_flag(task_thread_info(next),
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TIF_FOREIGN_FPSTATE);
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}
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}
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void fpsimd_flush_thread(void)
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{
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if (!system_supports_fpsimd())
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return;
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local_bh_disable();
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memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
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fpsimd_flush_task_state(current);
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set_thread_flag(TIF_FOREIGN_FPSTATE);
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local_bh_enable();
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}
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/*
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* Save the userland FPSIMD state of 'current' to memory, but only if the state
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* currently held in the registers does in fact belong to 'current'
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*/
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void fpsimd_preserve_current_state(void)
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{
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if (!system_supports_fpsimd())
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return;
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local_bh_disable();
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if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
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fpsimd_save_state(¤t->thread.fpsimd_state);
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local_bh_enable();
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}
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/*
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* Load the userland FPSIMD state of 'current' from memory, but only if the
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* FPSIMD state already held in the registers is /not/ the most recent FPSIMD
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* state of 'current'
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*/
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void fpsimd_restore_current_state(void)
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{
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if (!system_supports_fpsimd())
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return;
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local_bh_disable();
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if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
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struct fpsimd_state *st = ¤t->thread.fpsimd_state;
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fpsimd_load_state(st);
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__this_cpu_write(fpsimd_last_state, st);
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st->cpu = smp_processor_id();
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}
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local_bh_enable();
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}
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/*
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* Load an updated userland FPSIMD state for 'current' from memory and set the
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* flag that indicates that the FPSIMD register contents are the most recent
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* FPSIMD state of 'current'
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*/
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void fpsimd_update_current_state(struct fpsimd_state *state)
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{
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if (!system_supports_fpsimd())
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return;
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local_bh_disable();
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fpsimd_load_state(state);
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if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
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struct fpsimd_state *st = ¤t->thread.fpsimd_state;
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__this_cpu_write(fpsimd_last_state, st);
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st->cpu = smp_processor_id();
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}
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local_bh_enable();
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}
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/*
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* Invalidate live CPU copies of task t's FPSIMD state
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*/
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void fpsimd_flush_task_state(struct task_struct *t)
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{
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t->thread.fpsimd_state.cpu = NR_CPUS;
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}
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#ifdef CONFIG_KERNEL_MODE_NEON
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DEFINE_PER_CPU(bool, kernel_neon_busy);
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EXPORT_PER_CPU_SYMBOL(kernel_neon_busy);
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/*
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* Kernel-side NEON support functions
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*/
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/*
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* kernel_neon_begin(): obtain the CPU FPSIMD registers for use by the calling
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* context
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*
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* Must not be called unless may_use_simd() returns true.
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* Task context in the FPSIMD registers is saved back to memory as necessary.
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*
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* A matching call to kernel_neon_end() must be made before returning from the
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* calling context.
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*
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* The caller may freely use the FPSIMD registers until kernel_neon_end() is
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* called.
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*/
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void kernel_neon_begin(void)
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{
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if (WARN_ON(!system_supports_fpsimd()))
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return;
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BUG_ON(!may_use_simd());
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local_bh_disable();
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__this_cpu_write(kernel_neon_busy, true);
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/* Save unsaved task fpsimd state, if any: */
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if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
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fpsimd_save_state(¤t->thread.fpsimd_state);
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/* Invalidate any task state remaining in the fpsimd regs: */
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__this_cpu_write(fpsimd_last_state, NULL);
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preempt_disable();
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local_bh_enable();
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}
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EXPORT_SYMBOL(kernel_neon_begin);
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/*
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* kernel_neon_end(): give the CPU FPSIMD registers back to the current task
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*
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* Must be called from a context in which kernel_neon_begin() was previously
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* called, with no call to kernel_neon_end() in the meantime.
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*
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* The caller must not use the FPSIMD registers after this function is called,
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* unless kernel_neon_begin() is called again in the meantime.
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*/
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void kernel_neon_end(void)
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{
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bool busy;
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if (!system_supports_fpsimd())
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return;
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busy = __this_cpu_xchg(kernel_neon_busy, false);
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WARN_ON(!busy); /* No matching kernel_neon_begin()? */
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preempt_enable();
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}
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EXPORT_SYMBOL(kernel_neon_end);
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#ifdef CONFIG_EFI
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static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state);
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static DEFINE_PER_CPU(bool, efi_fpsimd_state_used);
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/*
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* EFI runtime services support functions
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*
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* The ABI for EFI runtime services allows EFI to use FPSIMD during the call.
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* This means that for EFI (and only for EFI), we have to assume that FPSIMD
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* is always used rather than being an optional accelerator.
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*
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* These functions provide the necessary support for ensuring FPSIMD
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* save/restore in the contexts from which EFI is used.
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*
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* Do not use them for any other purpose -- if tempted to do so, you are
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* either doing something wrong or you need to propose some refactoring.
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*/
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/*
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* __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call
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*/
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void __efi_fpsimd_begin(void)
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{
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if (!system_supports_fpsimd())
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return;
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WARN_ON(preemptible());
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if (may_use_simd())
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kernel_neon_begin();
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else {
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fpsimd_save_state(this_cpu_ptr(&efi_fpsimd_state));
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__this_cpu_write(efi_fpsimd_state_used, true);
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}
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}
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/*
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* __efi_fpsimd_end(): clean up FPSIMD after an EFI runtime services call
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*/
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void __efi_fpsimd_end(void)
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{
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if (!system_supports_fpsimd())
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return;
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if (__this_cpu_xchg(efi_fpsimd_state_used, false))
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fpsimd_load_state(this_cpu_ptr(&efi_fpsimd_state));
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else
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kernel_neon_end();
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}
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#endif /* CONFIG_EFI */
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#endif /* CONFIG_KERNEL_MODE_NEON */
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#ifdef CONFIG_CPU_PM
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static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
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unsigned long cmd, void *v)
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{
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switch (cmd) {
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case CPU_PM_ENTER:
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if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
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fpsimd_save_state(¤t->thread.fpsimd_state);
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this_cpu_write(fpsimd_last_state, NULL);
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break;
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case CPU_PM_EXIT:
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if (current->mm)
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set_thread_flag(TIF_FOREIGN_FPSTATE);
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break;
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case CPU_PM_ENTER_FAILED:
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default:
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return NOTIFY_DONE;
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}
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return NOTIFY_OK;
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}
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static struct notifier_block fpsimd_cpu_pm_notifier_block = {
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.notifier_call = fpsimd_cpu_pm_notifier,
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};
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static void __init fpsimd_pm_init(void)
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{
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cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
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}
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#else
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static inline void fpsimd_pm_init(void) { }
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#endif /* CONFIG_CPU_PM */
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#ifdef CONFIG_HOTPLUG_CPU
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static int fpsimd_cpu_dead(unsigned int cpu)
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{
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per_cpu(fpsimd_last_state, cpu) = NULL;
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return 0;
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}
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static inline void fpsimd_hotplug_init(void)
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{
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cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead",
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NULL, fpsimd_cpu_dead);
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}
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#else
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static inline void fpsimd_hotplug_init(void) { }
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#endif
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/*
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* FP/SIMD support code initialisation.
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*/
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static int __init fpsimd_init(void)
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{
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if (elf_hwcap & HWCAP_FP) {
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fpsimd_pm_init();
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fpsimd_hotplug_init();
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} else {
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pr_notice("Floating-point is not implemented\n");
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}
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if (!(elf_hwcap & HWCAP_ASIMD))
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pr_notice("Advanced SIMD is not implemented\n");
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return 0;
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}
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core_initcall(fpsimd_init);
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