| Message ID | 20160923061826.30790-3-cyrilbur@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Fri, 2016-23-09 at 06:18:08 UTC, Cyril Bur wrote: > Comment from arch/powerpc/kernel/process.c:967: > If userspace is inside a transaction (whether active or > suspended) and FP/VMX/VSX instructions have ever been enabled > inside that transaction, then we have to keep them enabled > and keep the FP/VMX/VSX state loaded while ever the transaction > continues. The reason is that if we didn't, and subsequently > got a FP/VMX/VSX unavailable interrupt inside a transaction, > we don't know whether it's the same transaction, and thus we > don't know which of the checkpointed state and the ransactional > state to use. > > restore_math() restore_fp() and restore_altivec() currently may not > restore the registers. It doesn't appear that this is more serious > than a performance penalty. If the math registers aren't restored the > userspace thread will still be run with the facility disabled. > Userspace will not be able to read invalid values. On the first access > it will take an facility unavailable exception and the kernel will > detected an active transaction, at which point it will abort the > transaction. There is the possibility for a pathological case > preventing any progress by transactions, however, transactions > are never guaranteed to make progress. > > Fixes: 70fe3d9 ("powerpc: Restore FPU/VEC/VSX if previously used") > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> Series applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/dc16b553c949e81f37555777dc7bab cheers
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index ce8a26a..3846fab 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -89,7 +89,13 @@ static void check_if_tm_restore_required(struct task_struct *tsk) set_thread_flag(TIF_RESTORE_TM); } } + +static inline bool msr_tm_active(unsigned long msr) +{ + return MSR_TM_ACTIVE(msr); +} #else +static inline bool msr_tm_active(unsigned long msr) { return false; } static inline void check_if_tm_restore_required(struct task_struct *tsk) { } #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */ @@ -209,7 +215,7 @@ void enable_kernel_fp(void) EXPORT_SYMBOL(enable_kernel_fp); static int restore_fp(struct task_struct *tsk) { - if (tsk->thread.load_fp) { + if (tsk->thread.load_fp || msr_tm_active(tsk->thread.regs->msr)) { load_fp_state(¤t->thread.fp_state); current->thread.load_fp++; return 1; @@ -279,7 +285,8 @@ EXPORT_SYMBOL_GPL(flush_altivec_to_thread); static int restore_altivec(struct task_struct *tsk) { - if (cpu_has_feature(CPU_FTR_ALTIVEC) && tsk->thread.load_vec) { + if (cpu_has_feature(CPU_FTR_ALTIVEC) && + (tsk->thread.load_vec || msr_tm_active(tsk->thread.regs->msr))) { load_vr_state(&tsk->thread.vr_state); tsk->thread.used_vr = 1; tsk->thread.load_vec++; @@ -465,7 +472,8 @@ void restore_math(struct pt_regs *regs) { unsigned long msr; - if (!current->thread.load_fp && !loadvec(current->thread)) + if (!msr_tm_active(regs->msr) && + !current->thread.load_fp && !loadvec(current->thread)) return; msr = regs->msr; @@ -984,6 +992,13 @@ void restore_tm_state(struct pt_regs *regs) msr_diff = current->thread.ckpt_regs.msr & ~regs->msr; msr_diff &= MSR_FP | MSR_VEC | MSR_VSX; + /* Ensure that restore_math() will restore */ + if (msr_diff & MSR_FP) + current->thread.load_fp = 1; +#ifdef CONFIG_ALIVEC + if (cpu_has_feature(CPU_FTR_ALTIVEC) && msr_diff & MSR_VEC) + current->thread.load_vec = 1; +#endif restore_math(regs); regs->msr |= msr_diff;
Comment from arch/powerpc/kernel/process.c:967: If userspace is inside a transaction (whether active or suspended) and FP/VMX/VSX instructions have ever been enabled inside that transaction, then we have to keep them enabled and keep the FP/VMX/VSX state loaded while ever the transaction continues. The reason is that if we didn't, and subsequently got a FP/VMX/VSX unavailable interrupt inside a transaction, we don't know whether it's the same transaction, and thus we don't know which of the checkpointed state and the ransactional state to use. restore_math() restore_fp() and restore_altivec() currently may not restore the registers. It doesn't appear that this is more serious than a performance penalty. If the math registers aren't restored the userspace thread will still be run with the facility disabled. Userspace will not be able to read invalid values. On the first access it will take an facility unavailable exception and the kernel will detected an active transaction, at which point it will abort the transaction. There is the possibility for a pathological case preventing any progress by transactions, however, transactions are never guaranteed to make progress. Fixes: 70fe3d9 ("powerpc: Restore FPU/VEC/VSX if previously used") Signed-off-by: Cyril Bur <cyrilbur@gmail.com> --- arch/powerpc/kernel/process.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-)