From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41VJRn2NNyzF3JM for ; Tue, 17 Jul 2018 21:47:32 +1000 (AEST) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6HBi4W8137771 for ; Tue, 17 Jul 2018 07:47:30 -0400 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0b-001b2d01.pphosted.com with ESMTP id 2k9dxj50hu-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 17 Jul 2018 07:47:30 -0400 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 17 Jul 2018 07:47:29 -0400 Date: Tue, 17 Jul 2018 17:17:22 +0530 From: Gautham R Shenoy To: "Gautham R. Shenoy" Cc: Michael Ellerman , Benjamin Herrenschmidt , Michael Neuling , Vaidyanathan Srinivasan , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Florian Weimer , Oleg Nesterov Subject: Re: [PATCH] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop. Reply-To: ego@linux.vnet.ibm.com References: <1531826849-31838-1-git-send-email-ego@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1531826849-31838-1-git-send-email-ego@linux.vnet.ibm.com> Message-Id: <20180717114722.GA27570@in.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Jul 17, 2018 at 04:57:29PM +0530, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" > > 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 > Cc: Oleg Nesterov > Cc: Michael Neuling > Cc: Michael Ellerman > Cc: Benjamin Herrenschmidt > Cc: Vaidyanathan Srinivasan > Signed-off-by: Gautham R. Shenoy > --- > 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 >