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x86/fpu: Remove fpu->initialized 

The struct fpu.initialized member is always set to one for user tasks
and zero for kernel tasks. This avoids saving/restoring the FPU
registers for kernel threads.

The ->initialized = 0 case for user tasks has been removed in previous
changes, for instance, by doing an explicit unconditional init at fork()
time for FPU-less systems which was otherwise delayed until the emulated
opcode.

The context switch code (switch_fpu_prepare() + switch_fpu_finish())
can't unconditionally save/restore registers for kernel threads. Not
only would it slow down the switch but also load a zeroed xcomp_bv for
XSAVES.

For kernel_fpu_begin() (+end) the situation is similar: EFI with runtime
services uses this before alternatives_patched is true. Which means that
this function is used too early and it wasn't the case before.

For those two cases, use current->mm to distinguish between user and
kernel thread. For kernel_fpu_begin() skip save/restore of the FPU
registers.

During the context switch into a kernel thread don't do anything. There
is no reason to save the FPU state of a kernel thread.

The reordering in __switch_to() is important because the current()
pointer needs to be valid before switch_fpu_finish() is invoked so ->mm
is seen of the new task instead the old one.

N.B.: fpu__save() doesn't need to check ->mm because it is called by
user tasks only.

 [ bp: Massage. ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aubrey Li <aubrey.li@intel.com>
Cc: Babu Moger <Babu.Moger@amd.com>
Cc: "Chang S. Bae" <chang.seok.bae@intel.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nicolai Stange <nstange@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-8-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2019-04-03 18:41:36 +02:00 committed by Borislav Petkov
parent 39388e80f9
commit 2722146eb7
12 changed files with 53 additions and 121 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
arch/x86/ia32/ia32_signal.c
View File

@ -216,8 +216,7 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
size_t frame_size,
void __user **fpstate)
{
struct fpu *fpu = &current->thread.fpu;
unsigned long sp;
unsigned long sp, fx_aligned, math_size;
/* Default to using normal stack */
sp = regs->sp;
@ -231,15 +230,11 @@ static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs,
ksig->ka.sa.sa_restorer)
sp = (unsigned long) ksig->ka.sa.sa_restorer;
if (fpu->initialized) {
unsigned long fx_aligned, math_size;
sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size);
*fpstate = (struct _fpstate_32 __user *) sp;
if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned,
math_size) < 0)
return (void __user *) -1L;
}
sp = fpu__alloc_mathframe(sp, 1, &fx_aligned, &math_size);
*fpstate = (struct _fpstate_32 __user *) sp;
if (copy_fpstate_to_sigframe(*fpstate, (void __user *)fx_aligned,
math_size) < 0)
return (void __user *) -1L;
sp -= frame_size;
/* Align the stack pointer according to the i386 ABI,

18
arch/x86/include/asm/fpu/internal.h
View File

@ -494,11 +494,14 @@ static inline void fpregs_activate(struct fpu *fpu)
*
* - switch_fpu_finish() restores the new state as
* necessary.
*
* The FPU context is only stored/restored for a user task and
* ->mm is used to distinguish between kernel and user threads.
*/
static inline void
switch_fpu_prepare(struct fpu *old_fpu, int cpu)
{
if (static_cpu_has(X86_FEATURE_FPU) && old_fpu->initialized) {
if (static_cpu_has(X86_FEATURE_FPU) && current->mm) {
if (!copy_fpregs_to_fpstate(old_fpu))
old_fpu->last_cpu = -1;
else
@ -506,8 +509,7 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu)
/* But leave fpu_fpregs_owner_ctx! */
trace_x86_fpu_regs_deactivated(old_fpu);
} else
old_fpu->last_cpu = -1;
}
}
/*
@ -520,12 +522,12 @@ switch_fpu_prepare(struct fpu *old_fpu, int cpu)
*/
static inline void switch_fpu_finish(struct fpu *new_fpu, int cpu)
{
bool preload = static_cpu_has(X86_FEATURE_FPU) &&
new_fpu->initialized;
if (static_cpu_has(X86_FEATURE_FPU)) {
if (!fpregs_state_valid(new_fpu, cpu)) {
if (current->mm)
copy_kernel_to_fpregs(&new_fpu->state);
}
if (preload) {
if (!fpregs_state_valid(new_fpu, cpu))
copy_kernel_to_fpregs(&new_fpu->state);
fpregs_activate(new_fpu);
}
}

9
arch/x86/include/asm/fpu/types.h
View File

@ -293,15 +293,6 @@ struct fpu {
*/
unsigned int last_cpu;
/*
* @initialized:
*
* This flag indicates whether this context is initialized: if the task
* is not running then we can restore from this context, if the task
* is running then we should save into this context.
*/
unsigned char initialized;
/*
* @avx512_timestamp:
*

5
arch/x86/include/asm/trace/fpu.h
View File

@ -13,22 +13,19 @@ DECLARE_EVENT_CLASS(x86_fpu,
TP_STRUCT__entry(
__field(struct fpu *, fpu)
__field(bool, initialized)
__field(u64, xfeatures)
__field(u64, xcomp_bv)
),
TP_fast_assign(
__entry->fpu = fpu;
__entry->initialized = fpu->initialized;
if (boot_cpu_has(X86_FEATURE_OSXSAVE)) {
__entry->xfeatures = fpu->state.xsave.header.xfeatures;
__entry->xcomp_bv = fpu->state.xsave.header.xcomp_bv;
}
),
TP_printk("x86/fpu: %p initialized: %d xfeatures: %llx xcomp_bv: %llx",
TP_printk("x86/fpu: %p xfeatures: %llx xcomp_bv: %llx",
__entry->fpu,
__entry->initialized,
__entry->xfeatures,
__entry->xcomp_bv
)

70
arch/x86/kernel/fpu/core.c
View File

@ -101,7 +101,7 @@ static void __kernel_fpu_begin(void)
kernel_fpu_disable();
if (fpu->initialized) {
if (current->mm) {
/*
* Ignore return value -- we don't care if reg state
* is clobbered.
@ -116,7 +116,7 @@ static void __kernel_fpu_end(void)
{
struct fpu *fpu = &current->thread.fpu;
if (fpu->initialized)
if (current->mm)
copy_kernel_to_fpregs(&fpu->state);
kernel_fpu_enable();
@ -147,11 +147,10 @@ void fpu__save(struct fpu *fpu)
preempt_disable();
trace_x86_fpu_before_save(fpu);
if (fpu->initialized) {
if (!copy_fpregs_to_fpstate(fpu)) {
copy_kernel_to_fpregs(&fpu->state);
}
}
if (!copy_fpregs_to_fpstate(fpu))
copy_kernel_to_fpregs(&fpu->state);
trace_x86_fpu_after_save(fpu);
preempt_enable();
}
@ -190,7 +189,7 @@ int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
{
dst_fpu->last_cpu = -1;
if (!src_fpu->initialized || !static_cpu_has(X86_FEATURE_FPU))
if (!static_cpu_has(X86_FEATURE_FPU))
return 0;
WARN_ON_FPU(src_fpu != &current->thread.fpu);
@ -227,14 +226,10 @@ static void fpu__initialize(struct fpu *fpu)
{
WARN_ON_FPU(fpu != &current->thread.fpu);
if (!fpu->initialized) {
fpstate_init(&fpu->state);
trace_x86_fpu_init_state(fpu);
fpstate_init(&fpu->state);
trace_x86_fpu_init_state(fpu);
trace_x86_fpu_activate_state(fpu);
/* Safe to do for the current task: */
fpu->initialized = 1;
}
trace_x86_fpu_activate_state(fpu);
}
/*
@ -247,32 +242,20 @@ static void fpu__initialize(struct fpu *fpu)
*
* - or it's called for stopped tasks (ptrace), in which case the
* registers were already saved by the context-switch code when
* the task scheduled out - we only have to initialize the registers
* if they've never been initialized.
* the task scheduled out.
*
* If the task has used the FPU before then save it.
*/
void fpu__prepare_read(struct fpu *fpu)
{
if (fpu == &current->thread.fpu) {
if (fpu == &current->thread.fpu)
fpu__save(fpu);
} else {
if (!fpu->initialized) {
fpstate_init(&fpu->state);
trace_x86_fpu_init_state(fpu);
trace_x86_fpu_activate_state(fpu);
/* Safe to do for current and for stopped child tasks: */
fpu->initialized = 1;
}
}
}
/*
* This function must be called before we write a task's fpstate.
*
* If the task has used the FPU before then invalidate any cached FPU registers.
* If the task has not used the FPU before then initialize its fpstate.
* Invalidate any cached FPU registers.
*
* After this function call, after registers in the fpstate are
* modified and the child task has woken up, the child task will
@ -289,17 +272,8 @@ void fpu__prepare_write(struct fpu *fpu)
*/
WARN_ON_FPU(fpu == &current->thread.fpu);
if (fpu->initialized) {
/* Invalidate any cached state: */
__fpu_invalidate_fpregs_state(fpu);
} else {
fpstate_init(&fpu->state);
trace_x86_fpu_init_state(fpu);
trace_x86_fpu_activate_state(fpu);
/* Safe to do for stopped child tasks: */
fpu->initialized = 1;
}
/* Invalidate any cached state: */
__fpu_invalidate_fpregs_state(fpu);
}
/*
@ -316,17 +290,13 @@ void fpu__drop(struct fpu *fpu)
preempt_disable();
if (fpu == &current->thread.fpu) {
if (fpu->initialized) {
/* Ignore delayed exceptions from user space */
asm volatile("1: fwait\n"
"2:\n"
_ASM_EXTABLE(1b, 2b));
fpregs_deactivate(fpu);
}
/* Ignore delayed exceptions from user space */
asm volatile("1: fwait\n"
"2:\n"
_ASM_EXTABLE(1b, 2b));
fpregs_deactivate(fpu);
}
fpu->initialized = 0;
trace_x86_fpu_dropped(fpu);
preempt_enable();

2
arch/x86/kernel/fpu/init.c
View File

@ -239,8 +239,6 @@ static void __init fpu__init_system_ctx_switch(void)
WARN_ON_FPU(!on_boot_cpu);
on_boot_cpu = 0;
WARN_ON_FPU(current->thread.fpu.initialized);
}
/*

19
arch/x86/kernel/fpu/regset.c
View File

@ -15,16 +15,12 @@
*/
int regset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
{
struct fpu *target_fpu = &target->thread.fpu;
return target_fpu->initialized ? regset->n : 0;
return regset->n;
}
int regset_xregset_fpregs_active(struct task_struct *target, const struct user_regset *regset)
{
struct fpu *target_fpu = &target->thread.fpu;
if (boot_cpu_has(X86_FEATURE_FXSR) && target_fpu->initialized)
if (boot_cpu_has(X86_FEATURE_FXSR))
return regset->n;
else
return 0;
@ -370,16 +366,9 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
int dump_fpu(struct pt_regs *regs, struct user_i387_struct *ufpu)
{
struct task_struct *tsk = current;
struct fpu *fpu = &tsk->thread.fpu;
int fpvalid;
fpvalid = fpu->initialized;
if (fpvalid)
fpvalid = !fpregs_get(tsk, NULL,
0, sizeof(struct user_i387_ia32_struct),
ufpu, NULL);
return fpvalid;
return !fpregs_get(tsk, NULL, 0, sizeof(struct user_i387_ia32_struct),
ufpu, NULL);
}
EXPORT_SYMBOL(dump_fpu);

2
arch/x86/kernel/fpu/xstate.c
View File

@ -892,8 +892,6 @@ const void *get_xsave_field_ptr(int xsave_state)
{
struct fpu *fpu = &current->thread.fpu;
if (!fpu->initialized)
return NULL;
/*
* fpu__save() takes the CPU's xstate registers
* and saves them off to the 'fpu memory buffer.

4
arch/x86/kernel/process_32.c
View File

@ -288,10 +288,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
if (prev->gs | next->gs)
lazy_load_gs(next->gs);
switch_fpu_finish(next_fpu, cpu);
this_cpu_write(current_task, next_p);
switch_fpu_finish(next_fpu, cpu);
/* Load the Intel cache allocation PQR MSR. */
resctrl_sched_in();

4
arch/x86/kernel/process_64.c
View File

@ -566,14 +566,14 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
x86_fsgsbase_load(prev, next);
switch_fpu_finish(next_fpu, cpu);
/*
* Switch the PDA and FPU contexts.
*/
this_cpu_write(current_task, next_p);
this_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
switch_fpu_finish(next_fpu, cpu);
/* Reload sp0. */
update_task_stack(next_p);

17
arch/x86/kernel/signal.c
View File

@ -246,7 +246,7 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
unsigned long sp = regs->sp;
unsigned long buf_fx = 0;
int onsigstack = on_sig_stack(sp);
struct fpu *fpu = &current->thread.fpu;
int ret;
/* redzone */
if (IS_ENABLED(CONFIG_X86_64))
@ -265,11 +265,9 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
sp = (unsigned long) ka->sa.sa_restorer;
}
if (fpu->initialized) {
sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32),
&buf_fx, &math_size);
*fpstate = (void __user *)sp;
}
sp = fpu__alloc_mathframe(sp, IS_ENABLED(CONFIG_X86_32),
&buf_fx, &math_size);
*fpstate = (void __user *)sp;
sp = align_sigframe(sp - frame_size);
@ -281,8 +279,8 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
return (void __user *)-1L;
/* save i387 and extended state */
if (fpu->initialized &&
copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size) < 0)
ret = copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size);
if (ret < 0)
return (void __user *)-1L;
return (void __user *)sp;
@ -763,8 +761,7 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
/*
* Ensure the signal handler starts with the new fpu state.
*/
if (fpu->initialized)
fpu__clear(fpu);
fpu__clear(fpu);
}
signal_setup_done(failed, ksig, stepping);
}

7
arch/x86/mm/pkeys.c
View File

@ -39,17 +39,12 @@ int __execute_only_pkey(struct mm_struct *mm)
* dance to set PKRU if we do not need to. Check it
* first and assume that if the execute-only pkey is
* write-disabled that we do not have to set it
* ourselves. We need preempt off so that nobody
* can make fpregs inactive.
* ourselves.
*/
preempt_disable();
if (!need_to_set_mm_pkey &&
current->thread.fpu.initialized &&
!__pkru_allows_read(read_pkru(), execute_only_pkey)) {
preempt_enable();
return execute_only_pkey;
}
preempt_enable();
/*
* Set up PKRU so that it denies access for everything