From: Akihiko Odaki <akihiko.odaki@daynix.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] accel/kvm/kvm-all: Handle register access errors
Date: Thu, 1 Dec 2022 20:00:22 +0900 [thread overview]
Message-ID: <a3cc1116-272d-a8e5-a131-7becf98115e0@daynix.com> (raw)
In-Reply-To: <CAFEAcA_ORM9CpDCvPMs1XcZVhh_4fKE2wnaS_tp1s4DzZCHsXQ@mail.gmail.com>
On 2022/12/01 19:40, Peter Maydell wrote:
> On Thu, 1 Dec 2022 at 10:27, Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>>
>> A register access error typically means something seriously wrong
>> happened so that anything bad can happen after that and recovery is
>> impossible.
>> Even failing one register access is catastorophic as
>> architecture-specific code are not written so that it torelates such
>> failures.
>>
>> Make sure the VM stop and nothing worse happens if such an error occurs.
>>
>> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>
> In a similar vein there was also
> https://lore.kernel.org/all/20220617144857.34189-1-peterx@redhat.com/
> back in June, which on the one hand was less comprehensive but on
> the other does the plumbing to pass the error upwards rather than
> reporting it immediately at point of failure.
>
> I'm in principle in favour but suspect we'll run into some corner
> cases where we were happily ignoring not-very-important failures
> (eg if you're running Linux as the host OS on a Mac M1 and your
> host kernel doesn't have this fix:
> https://lore.kernel.org/all/YnHz6Cw5ONR2e+KA@google.com/T/
> then QEMU will go from "works by sheer luck" to "consistently
> hits this error check"). So we should aim to land this extra
> error checking early in the release cycle so we have plenty of
> time to deal with any bug reports we get about it.
>
> thanks
> -- PMM
Actually I found this problem when I tried to run QEMU with KVM on M2
MacBook Air and encountered a failure described and fixed at:
https://lore.kernel.org/all/20221201104914.28944-2-akihiko.odaki@daynix.com/
Although the affected register was not really important, QEMU couldn't
run the guest well enough because kvm_arch_put_registers for ARM64 is
written in a way that it fails early. I guess the situation is not so
different for other architectures as well.
I still agree that this should be postponed until a new release cycle
starts as register saving/restoring is too important to fail.
Regards,
Akihiko Odaki
next prev parent reply other threads:[~2022-12-01 11:01 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-01 10:27 [PATCH] accel/kvm/kvm-all: Handle register access errors Akihiko Odaki
2022-12-01 10:40 ` Peter Maydell
2022-12-01 11:00 ` Akihiko Odaki [this message]
2022-12-01 11:19 ` Peter Maydell
2023-06-10 3:51 ` Akihiko Odaki
2023-06-19 12:19 ` Peter Maydell
2023-09-21 7:25 ` Akihiko Odaki
2023-09-21 13:33 ` Peter Maydell
2023-09-27 10:04 ` Paolo Bonzini
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