From: Michael Ellerman <mpe@ellerman.id.au> To: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Christophe Leroy <christophe.leroy@c-s.fr>, paulus@samba.org, npiggin@gmail.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org Subject: Re: [PATCH] powerpc: fix 32-bit KVM-PR lockup and panic with MacOS guest Date: Tue, 19 Feb 2019 15:55:10 +1100 [thread overview] Message-ID: <87mumsbcnl.fsf@concordia.ellerman.id.au> (raw) In-Reply-To: <46205b6a-7671-5d90-9507-b5b20045b99d@ilande.co.uk> Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> writes: > On 11/02/2019 00:30, Benjamin Herrenschmidt wrote: > >> On Fri, 2019-02-08 at 14:51 +0000, Mark Cave-Ayland wrote: >>> >>> Indeed, but there are still some questions to be asked here: >>> >>> 1) Why were these bits removed from the original bitmask in the first place without >>> it being documented in the commit message? >>> >>> 2) Is this the right fix? I'm told that MacOS guests already run without this patch >>> on a G5 under 64-bit KVM-PR which may suggest that this is a workaround for another >>> bug elsewhere in the 32-bit powerpc code. >>> >>> >>> If you think that these points don't matter, then I'm happy to resubmit the patch >>> as-is based upon your comments above. >> >> We should write a test case to verify that FE0/FE1 are properly >> preserved/context-switched etc... I bet if we accidentally wiped them, >> we wouldn't notice 99.9% of the time. > > Right I guess it's more likely to cause in issue in the KVM PR case because the guest > can alter the flags in a way that doesn't go through the normal process switch mechanism. > > The original patchset at > https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg98326.html does include > some tests in the first few patches, but AFAICT they are concerned with the contents > of the FP registers rather than the related MSRs. fpu_preempt.c should be able to be adapted to also check the MSR bits. > Who is the right person to ask about fixing issues related to context switching with > KVM PR? KVM PR doesn't really have a maintainer TBH. Feel like volunteering? :) > I did add the original author's email address to my first few emails but have > had no response back :/ Cyril who wrote the original FPU patch has moved on to other things. cheers
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From: Michael Ellerman <mpe@ellerman.id.au> To: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Christophe Leroy <christophe.leroy@c-s.fr>, paulus@samba.org, npiggin@gmail.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org Subject: Re: [PATCH] powerpc: fix 32-bit KVM-PR lockup and panic with MacOS guest Date: Tue, 19 Feb 2019 04:55:10 +0000 [thread overview] Message-ID: <87mumsbcnl.fsf@concordia.ellerman.id.au> (raw) In-Reply-To: <46205b6a-7671-5d90-9507-b5b20045b99d@ilande.co.uk> Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> writes: > On 11/02/2019 00:30, Benjamin Herrenschmidt wrote: > >> On Fri, 2019-02-08 at 14:51 +0000, Mark Cave-Ayland wrote: >>> >>> Indeed, but there are still some questions to be asked here: >>> >>> 1) Why were these bits removed from the original bitmask in the first place without >>> it being documented in the commit message? >>> >>> 2) Is this the right fix? I'm told that MacOS guests already run without this patch >>> on a G5 under 64-bit KVM-PR which may suggest that this is a workaround for another >>> bug elsewhere in the 32-bit powerpc code. >>> >>> >>> If you think that these points don't matter, then I'm happy to resubmit the patch >>> as-is based upon your comments above. >> >> We should write a test case to verify that FE0/FE1 are properly >> preserved/context-switched etc... I bet if we accidentally wiped them, >> we wouldn't notice 99.9% of the time. > > Right I guess it's more likely to cause in issue in the KVM PR case because the guest > can alter the flags in a way that doesn't go through the normal process switch mechanism. > > The original patchset at > https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg98326.html does include > some tests in the first few patches, but AFAICT they are concerned with the contents > of the FP registers rather than the related MSRs. fpu_preempt.c should be able to be adapted to also check the MSR bits. > Who is the right person to ask about fixing issues related to context switching with > KVM PR? KVM PR doesn't really have a maintainer TBH. Feel like volunteering? :) > I did add the original author's email address to my first few emails but have > had no response back :/ Cyril who wrote the original FPU patch has moved on to other things. cheers
next prev parent reply other threads:[~2019-02-19 4:55 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-08 14:33 [PATCH] powerpc: fix 32-bit KVM-PR lockup and panic with MacOS guest Mark Cave-Ayland 2019-02-08 14:33 ` Mark Cave-Ayland 2019-02-08 14:45 ` Christophe Leroy 2019-02-08 14:45 ` Christophe Leroy 2019-02-08 14:51 ` Mark Cave-Ayland 2019-02-08 14:51 ` Mark Cave-Ayland 2019-02-11 0:30 ` Benjamin Herrenschmidt 2019-02-11 0:30 ` Benjamin Herrenschmidt 2019-02-11 21:39 ` Mark Cave-Ayland 2019-02-19 4:55 ` Michael Ellerman [this message] 2019-02-19 4:55 ` Michael Ellerman 2019-02-19 8:15 ` Mark Cave-Ayland 2019-02-19 4:20 ` Michael Ellerman 2019-02-19 4:20 ` Michael Ellerman 2019-02-19 7:55 ` Mark Cave-Ayland 2019-02-20 12:41 ` Michael Ellerman 2019-02-20 12:41 ` Michael Ellerman 2019-02-19 19:31 ` Cameron Kaiser 2019-02-22 9:47 ` Michael Ellerman 2019-02-22 9:47 ` Michael Ellerman
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