Re: [PATCH] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop.
From: Gautham R Shenoy <hidden>
Date: 2018-07-17 11:47:33
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On Tue, Jul 17, 2018 at 04:57:29PM +0530, Gautham R. Shenoy wrote:
From: "Gautham R. Shenoy" <redacted> On 64-bit Servers, SPRN_SPRG3 and its userspace read-only mirror SPRN_USPRG3 are used as userspace VDSO write and read registers respectively.
SPRN_SPRG3 is lost when we enter stop4 and above, and is currently not restored. As a result, any read from SPRN_USPRG3 returns zero on an exit from stop4 and above. Thus in this situation, any call from sched_getcpu() always returns
This happens only on POWER9.
zero, as on powerpc, we call __kernel_getcpu() which relies upon SPRN_USPRG3 to report the CPU and NUMA node information. Fix this by saving the SPRN_SPRG3 before entering a deep stop state, and restoring it back on wakeup from the stop state.
I forgot to add that this fixes commit e1c1cfed5432 ("powerpc/powernv:
Save/Restore additional SPRs for stop4 cpuidle").
@mpe, do you want me to send fresh patch with these updates ?
quoted hunk ↗ jump to hunk
Reported-by: Florian Weimer <redacted> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Michael Neuling <redacted> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Vaidyanathan Srinivasan <redacted> Signed-off-by: Gautham R. Shenoy <redacted> --- arch/powerpc/include/asm/cpuidle.h | 1 + arch/powerpc/kernel/asm-offsets.c | 1 + arch/powerpc/kernel/idle_book3s.S | 5 +++++ 3 files changed, 7 insertions(+)diff --git a/arch/powerpc/include/asm/cpuidle.h b/arch/powerpc/include/asm/cpuidle.h index e210a83..03fa904 100644 --- a/arch/powerpc/include/asm/cpuidle.h +++ b/arch/powerpc/include/asm/cpuidle.h@@ -77,6 +77,7 @@ struct stop_sprs { u64 mmcr1; u64 mmcr2; u64 mmcra; + u64 sprg3; }; extern u32 pnv_fastsleep_workaround_at_entry[];diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 89cf155..a35ebfc 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c@@ -776,6 +776,7 @@ int main(void) STOP_SPR(STOP_MMCR1, mmcr1); STOP_SPR(STOP_MMCR2, mmcr2); STOP_SPR(STOP_MMCRA, mmcra); + STOP_SPR(STOP_SPRG3, sprg3); #endif DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S index d85d551..5069d42 100644 --- a/arch/powerpc/kernel/idle_book3s.S +++ b/arch/powerpc/kernel/idle_book3s.S@@ -120,6 +120,9 @@ power9_save_additional_sprs: mfspr r4, SPRN_MMCR2 std r3, STOP_MMCR1(r13) std r4, STOP_MMCR2(r13) + + mfspr r3, SPRN_SPRG3 + std r3, STOP_SPRG3(r13) blr power9_restore_additional_sprs:@@ -144,7 +147,9 @@ power9_restore_additional_sprs: mtspr SPRN_MMCR1, r4 ld r3, STOP_MMCR2(r13) + ld r4, STOP_SPRG3(r13) mtspr SPRN_MMCR2, r3 + mtspr SPRN_SPRG3, r4 blr /*-- 1.9.4