On Tue, Jul 17, 2018 at 04:57:29PM +0530, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
>
> 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 ?
> Reported-by: Florian Weimer <fwei...@redhat.com>
> Cc: Oleg Nesterov <o...@redhat.com>
> Cc: Michael Neuling <mi...@neuling.org>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Cc: Vaidyanathan Srinivasan <sva...@linux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> ---
> 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
>
