From 96d016108640bc2b7fb0ee800737f80923847294 Mon Sep 17 00:00:00 2001 From: Sam bobroff Date: Thu, 5 Jun 2014 16:19:22 +1000 Subject: powerpc: Correct DSCR during TM context switch Correct the DSCR SPR becoming temporarily corrupted if a task is context switched during a transaction. The problem occurs while suspending the task and is caused by saving the DSCR to thread.dscr after it has already been set to the CPU's default value: __switch_to() calls __switch_to_tm() which calls tm_reclaim_task() which calls tm_reclaim_thread() which calls tm_reclaim() where the DSCR is set to the CPU's default __switch_to() calls _switch() where thread.dscr is set to the DSCR When the task is resumed, it's transaction will be doomed (as usual) and the DSCR SPR will be corrupted, although the checkpointed value will be correct. Therefore the DSCR will be immediately corrected by the transaction aborting, unless it has been suspended. In that case the incorrect value can be seen by the task until it resumes the transaction. The fix is to treat the DSCR similarly to the TAR and save it early in __switch_to(). A program exposing the problem is added to the kernel self tests as: tools/testing/selftests/powerpc/tm/tm-resched-dscr. Signed-off-by: Sam Bobroff CC: [v3.10+] Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/switch_to.h | 6 ++++-- arch/powerpc/kernel/entry_64.S | 6 ------ arch/powerpc/kernel/process.c | 8 ++++---- 3 files changed, 8 insertions(+), 12 deletions(-) (limited to 'arch') diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index 0e83e7d8c73f..d2468eb12639 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -16,13 +16,15 @@ struct thread_struct; extern struct task_struct *_switch(struct thread_struct *prev, struct thread_struct *next); #ifdef CONFIG_PPC_BOOK3S_64 -static inline void save_tar(struct thread_struct *prev) +static inline void save_early_sprs(struct thread_struct *prev) { if (cpu_has_feature(CPU_FTR_ARCH_207S)) prev->tar = mfspr(SPRN_TAR); + if (cpu_has_feature(CPU_FTR_DSCR)) + prev->dscr = mfspr(SPRN_DSCR); } #else -static inline void save_tar(struct thread_struct *prev) {} +static inline void save_early_sprs(struct thread_struct *prev) {} #endif extern void enable_kernel_fp(void); diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 911d45366f59..6528c5e2cc44 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -428,12 +428,6 @@ BEGIN_FTR_SECTION std r24,THREAD_VRSAVE(r3) END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) #endif /* CONFIG_ALTIVEC */ -#ifdef CONFIG_PPC64 -BEGIN_FTR_SECTION - mfspr r25,SPRN_DSCR - std r25,THREAD_DSCR(r3) -END_FTR_SECTION_IFSET(CPU_FTR_DSCR) -#endif and. r0,r0,r22 beq+ 1f andc r22,r22,r0 diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 8a1edbe26b8f..be99774d3f44 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -755,15 +755,15 @@ struct task_struct *__switch_to(struct task_struct *prev, WARN_ON(!irqs_disabled()); - /* Back up the TAR across context switches. + /* Back up the TAR and DSCR across context switches. * Note that the TAR is not available for use in the kernel. (To * provide this, the TAR should be backed up/restored on exception * entry/exit instead, and be in pt_regs. FIXME, this should be in * pt_regs anyway (for debug).) - * Save the TAR here before we do treclaim/trecheckpoint as these - * will change the TAR. + * Save the TAR and DSCR here before we do treclaim/trecheckpoint as + * these will change them. */ - save_tar(&prev->thread); + save_early_sprs(&prev->thread); __switch_to_tm(prev); -- cgit v1.2.2