| From 644c154186386bb1fa6446bc5e037b9ed098db46 Mon Sep 17 00:00:00 2001 |
| From: Vincent Palatin <vpalatin@chromium.org> |
| Date: Fri, 30 Nov 2012 12:15:32 -0800 |
| Subject: x86, fpu: Avoid FPU lazy restore after suspend |
| |
| From: Vincent Palatin <vpalatin@chromium.org> |
| |
| commit 644c154186386bb1fa6446bc5e037b9ed098db46 upstream. |
| |
| When a cpu enters S3 state, the FPU state is lost. |
| After resuming for S3, if we try to lazy restore the FPU for a process running |
| on the same CPU, this will result in a corrupted FPU context. |
| |
| Ensure that "fpu_owner_task" is properly invalided when (re-)initializing a CPU, |
| so nobody will try to lazy restore a state which doesn't exist in the hardware. |
| |
| Tested with a 64-bit kernel on a 4-core Ivybridge CPU with eagerfpu=off, |
| by doing thousands of suspend/resume cycles with 4 processes doing FPU |
| operations running. Without the patch, a process is killed after a |
| few hundreds cycles by a SIGFPE. |
| |
| Signed-off-by: Vincent Palatin <vpalatin@chromium.org> |
| Cc: Duncan Laurie <dlaurie@chromium.org> |
| Cc: Olof Johansson <olofj@chromium.org> |
| Link: http://lkml.kernel.org/r/1354306532-1014-1-git-send-email-vpalatin@chromium.org |
| Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/include/asm/fpu-internal.h | 15 +++++++++------ |
| arch/x86/kernel/smpboot.c | 5 +++++ |
| 2 files changed, 14 insertions(+), 6 deletions(-) |
| |
| --- a/arch/x86/include/asm/fpu-internal.h |
| +++ b/arch/x86/include/asm/fpu-internal.h |
| @@ -334,14 +334,17 @@ static inline void __thread_fpu_begin(st |
| typedef struct { int preload; } fpu_switch_t; |
| |
| /* |
| - * FIXME! We could do a totally lazy restore, but we need to |
| - * add a per-cpu "this was the task that last touched the FPU |
| - * on this CPU" variable, and the task needs to have a "I last |
| - * touched the FPU on this CPU" and check them. |
| + * Must be run with preemption disabled: this clears the fpu_owner_task, |
| + * on this CPU. |
| * |
| - * We don't do that yet, so "fpu_lazy_restore()" always returns |
| - * false, but some day.. |
| + * This will disable any lazy FPU state restore of the current FPU state, |
| + * but if the current thread owns the FPU, it will still be saved by. |
| */ |
| +static inline void __cpu_disable_lazy_restore(unsigned int cpu) |
| +{ |
| + per_cpu(fpu_owner_task, cpu) = NULL; |
| +} |
| + |
| static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu) |
| { |
| return new == this_cpu_read_stable(fpu_owner_task) && |
| --- a/arch/x86/kernel/smpboot.c |
| +++ b/arch/x86/kernel/smpboot.c |
| @@ -68,6 +68,8 @@ |
| #include <asm/mwait.h> |
| #include <asm/apic.h> |
| #include <asm/io_apic.h> |
| +#include <asm/i387.h> |
| +#include <asm/fpu-internal.h> |
| #include <asm/setup.h> |
| #include <asm/uv/uv.h> |
| #include <linux/mc146818rtc.h> |
| @@ -817,6 +819,9 @@ int __cpuinit native_cpu_up(unsigned int |
| |
| per_cpu(cpu_state, cpu) = CPU_UP_PREPARE; |
| |
| + /* the FPU context is blank, nobody can own it */ |
| + __cpu_disable_lazy_restore(cpu); |
| + |
| err = do_boot_cpu(apicid, cpu, tidle); |
| if (err) { |
| pr_debug("do_boot_cpu failed %d\n", err); |