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powerpc/64s/exception: Avoid touching the stack in hdecrementer 

The hdec interrupt handler is reported to sometimes fire in Linux if
KVM leaves it pending after a guest exists. This is harmless, so there
is a no-op handler for it.

The interrupt handler currently uses the regular kernel stack. Change
this to avoid touching the stack entirely.

This should be the last place where the regular Linux stack can be
accessed with asynchronous interrupts (including PMI) soft-masked.
It might be possible to take advantage of this invariant, e.g., to
context switch the kernel stack SLB entry without clearing MSR[EE].

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200225173541.1549955-17-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2020-02-26 03:35:25 +10:00 committed by Michael Ellerman
parent 9d598f9344
commit 2babd6ea43
3 changed files with 20 additions and 15 deletions
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1
arch/powerpc/include/asm/time.h
View File

@ -24,7 +24,6 @@ extern struct clock_event_device decrementer_clockevent;
extern void generic_calibrate_decr(void);
extern void hdec_interrupt(struct pt_regs *regs);
/* Some sane defaults: 125 MHz timebase, 1GHz processor */
extern unsigned long ppc_proc_freq;

25
arch/powerpc/kernel/exceptions-64s.S
View File

@ -1507,6 +1507,8 @@ EXC_COMMON_BEGIN(decrementer_common)
INT_DEFINE_BEGIN(hdecrementer)
IVEC=0x980
IHSRR=EXC_HV
ISTACK=0
IRECONCILE=0
IKVM_REAL=1
IKVM_VIRT=1
INT_DEFINE_END(hdecrementer)
@ -1518,11 +1520,24 @@ EXC_VIRT_BEGIN(hdecrementer, 0x4980, 0x80)
GEN_INT_ENTRY hdecrementer, virt=1
EXC_VIRT_END(hdecrementer, 0x4980, 0x80)
EXC_COMMON_BEGIN(hdecrementer_common)
GEN_COMMON hdecrementer
bl save_nvgprs
addi r3,r1,STACK_FRAME_OVERHEAD
bl hdec_interrupt
b ret_from_except
__GEN_COMMON_ENTRY hdecrementer
/*
* Hypervisor decrementer interrupts not caught by the KVM test
* shouldn't occur but are sometimes left pending on exit from a KVM
* guest. We don't need to do anything to clear them, as they are
* edge-triggered.
*
* Be careful to avoid touching the kernel stack.
*/
ld r10,PACA_EXGEN+EX_CTR(r13)
mtctr r10
mtcrf 0x80,r9
ld r9,PACA_EXGEN+EX_R9(r13)
ld r10,PACA_EXGEN+EX_R10(r13)
ld r11,PACA_EXGEN+EX_R11(r13)
ld r12,PACA_EXGEN+EX_R12(r13)
ld r13,PACA_EXGEN+EX_R13(r13)
HRFI_TO_KERNEL
GEN_KVM hdecrementer

9
arch/powerpc/kernel/time.c
View File

@ -663,15 +663,6 @@ void timer_broadcast_interrupt(void)
}
#endif
/*
* Hypervisor decrementer interrupts shouldn't occur but are sometimes
* left pending on exit from a KVM guest. We don't need to do anything
* to clear them, as they are edge-triggered.
*/
void hdec_interrupt(struct pt_regs *regs)
{
}
#ifdef CONFIG_SUSPEND
static void generic_suspend_disable_irqs(void)
{