[RFC PATCH 10/12] [WIP] powerpc/tm: Correctly save/restore checkpointed sprs
Cyril Bur
cyrilbur at gmail.com
Tue Feb 20 11:22:39 AEDT 2018
---
arch/powerpc/kernel/process.c | 57 +++++++++++++++++++++++++++++++++++++++++--
arch/powerpc/kernel/ptrace.c | 9 +++----
2 files changed, 58 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index cd3ae80a6878..674f75c56172 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -859,6 +859,8 @@ static inline bool tm_enabled(struct task_struct *tsk)
return tsk && tsk->thread.regs && (tsk->thread.regs->msr & MSR_TM);
}
+static inline void save_sprs(struct thread_struct *t);
+
static void tm_reclaim_thread(struct thread_struct *thr, uint8_t cause)
{
/*
@@ -879,6 +881,8 @@ static void tm_reclaim_thread(struct thread_struct *thr, uint8_t cause)
if (!MSR_TM_SUSPENDED(mfmsr()))
return;
+ save_sprs(thr);
+
giveup_all(container_of(thr, struct task_struct, thread));
tm_reclaim(thr, cause);
@@ -991,6 +995,37 @@ void tm_recheckpoint(struct thread_struct *thread)
__tm_recheckpoint(thread);
+ /*
+ * This is a stripped down restore_sprs(), we need to do this
+ * now as we might go straight out to userspace and currently
+ * the checkpointed values are on the CPU.
+ *
+ * TODO: Improve
+ */
+#ifdef CONFIG_ALTIVEC
+ if (cpu_has_feature(CPU_FTR_ALTIVEC))
+ mtspr(SPRN_VRSAVE, thread->vrsave);
+#endif
+#ifdef CONFIG_PPC_BOOK3S_64
+ if (cpu_has_feature(CPU_FTR_DSCR)) {
+ u64 dscr = get_paca()->dscr_default;
+ if (thread->dscr_inherit)
+ dscr = thread->dscr;
+
+ mtspr(SPRN_DSCR, dscr);
+ }
+
+ if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
+ /* The EBB regs aren't checkpointed */
+ mtspr(SPRN_FSCR, thread->fscr);
+
+ mtspr(SPRN_TAR, thread->tar);
+ }
+
+ /* I think we don't need to */
+ if (cpu_has_feature(CPU_FTR_ARCH_300))
+ mtspr(SPRN_TIDR, thread->tidr);
+#endif
local_irq_restore(flags);
}
@@ -1193,6 +1228,11 @@ struct task_struct *__switch_to(struct task_struct *prev,
#endif
new_thread = &new->thread;
+ /*
+ * Why not &prev->thread; ?
+ * What is the difference between &prev->thread and
+ * ¤t->thread ?
+ */
old_thread = ¤t->thread;
WARN_ON(!irqs_disabled());
@@ -1237,8 +1277,16 @@ struct task_struct *__switch_to(struct task_struct *prev,
/*
* We need to save SPRs before treclaim/trecheckpoint as these will
* change a number of them.
+ *
+ * Because we're now reclaiming on kernel entry, we've had to
+ * already save them. Don't do it again.
+ * Note: To deliver a signal in the signal context, we'll have
+ * turned off TM because we don't want the signal context to
+ * have the transactional state of the main thread - what if
+ * we go through switch to at that point? Can we?
*/
- save_sprs(&prev->thread);
+ if (!prev->thread.regs || !MSR_TM_ACTIVE(prev->thread.regs->msr))
+ save_sprs(&prev->thread);
/* Save FPU, Altivec, VSX and SPE state */
giveup_all(prev);
@@ -1260,8 +1308,13 @@ struct task_struct *__switch_to(struct task_struct *prev,
* for this is we manually create a stack frame for new tasks that
* directly returns through ret_from_fork() or
* ret_from_kernel_thread(). See copy_thread() for details.
+ *
+ * It isn't stricly nessesary that we avoid the restore here
+ * because we'll simply restore again after the recheckpoint,
+ * but we can avoid it for performance reasons.
*/
- restore_sprs(old_thread, new_thread);
+ if (!new_thread->regs || !MSR_TM_ACTIVE(new_thread->regs->msr))
+ restore_sprs(old_thread, new_thread);
last = _switch(old_thread, new_thread);
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index ca72d7391d40..16001987ba71 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -135,12 +135,9 @@ static void flush_tmregs_to_thread(struct task_struct *tsk)
if ((!cpu_has_feature(CPU_FTR_TM)) || (tsk != current))
return;
- if (MSR_TM_SUSPENDED(mfmsr())) {
- tm_reclaim_current(TM_CAUSE_SIGNAL);
- } else {
- tm_enable();
- tm_save_sprs(&(tsk->thread));
- }
+ BUG_ON(MSR_TM_SUSPENDED(mfmsr()));
+ tm_enable();
+ tm_save_sprs(&(tsk->thread));
}
#else
static inline void flush_tmregs_to_thread(struct task_struct *tsk) { }
--
2.16.2
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