From: Mark Cave-Ayland <email@example.com> To: Michael Ellerman <firstname.lastname@example.org>, Christophe Leroy <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH] powerpc: fix 32-bit KVM-PR lockup and panic with MacOS guest Date: Tue, 19 Feb 2019 07:55:55 +0000 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 19/02/2019 04:20, Michael Ellerman wrote: Hi Michael, > Mark Cave-Ayland <firstname.lastname@example.org> writes: >> On 08/02/2019 14:45, Christophe Leroy wrote: >> >>> Le 08/02/2019 à 15:33, Mark Cave-Ayland a écrit : >>>> Commit 8792468da5e1 "powerpc: Add the ability to save FPU without giving it up" >>> >>> Expected format for the above is: >>> >>> Commit 123456789abc ("text") >> >> Hi Christophe, >> >> Apologies - I'm fairly new at submitting kernel patches, but I can re-send it in the >> correct format later if required. >> >>>> unexpectedly removed the MSR_FE0 and MSR_FE1 bits from the bitmask used to >>>> update the MSR of the previous thread in __giveup_fpu() causing a KVM-PR MacOS >>>> guest to lockup and panic the kernel. > > Which kernel is panicking? The guest or the host? It's the host kernel. As long as you occasionally tap a few keys to keep the screen blanking disabled then you can see the panic on the physical console. I've uploaded a photo I took during the bisection containing the panic when booting MacOS X 10.2 under qemu-system-ppc to https://www.ilande.co.uk/tmp/qemu/macmini-kvm.jpg in case you find it useful. Given that it's really easy to recreate, let me know if you want me to do a git pull/rebuild and/or if you need any debugging information as it's easy for me to reproduce. >>>> Reinstate these bits to the MSR bitmask to enable MacOS guests to run under >>>> 32-bit KVM-PR once again without issue. >>>> >>>> Signed-off-by: Mark Cave-Ayland <email@example.com> >>> >>> Should include a Fixes: and a Cc to stable ? >>> >>> Fixes: 8792468da5e1 ("powerpc: Add the ability to save FPU without giving it up") >>> Cc: firstname.lastname@example.org >> >> 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? > > It was almost certainly an accident. Heh, okay :) >> 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. > > That's slightly worrying. It's hard to say without more detail on why > the guest is crashing. > > I think your patch looks OK based just on the fact that it restores the > previous behaviour, so I'll pick it up and pass it through my usual > testing. If nothing breaks I'll merge it. That would be great! Does it need a CC to stable too? It would be great if this would get picked up in the next set of Debian ports kernels, for example. ATB, Mark.
next prev parent reply index Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-08 14:33 Mark Cave-Ayland 2019-02-08 14:45 ` Christophe Leroy 2019-02-08 14:51 ` Mark Cave-Ayland 2019-02-11 0:30 ` Benjamin Herrenschmidt 2019-02-11 21:39 ` Mark Cave-Ayland 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 7:55 ` Mark Cave-Ayland [this message] 2019-02-20 12:41 ` Michael Ellerman 2019-02-22 9:47 ` Michael Ellerman
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