linux-kernel - Re: Fwd: kvm: Windows Server 2003 VM fails to work on 6.1.44 (works fine on 6.1.43)

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Message-ID: <87o7j75g0g.fsf@redhat.com>
Date:   Wed, 16 Aug 2023 14:27:27 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Roman Mamedov <rm+bko@...anrm.net>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux KVM <kvm@...r.kernel.org>,
        Borislav Petkov (AMD) <bp@...en8.de>
Subject: Re: Fwd: kvm: Windows Server 2003 VM fails to work on 6.1.44 (works
 fine on 6.1.43)

Bagas Sanjaya <bagasdotme@...il.com> writes:

> Hi,
>
> I notice a regression report on Bugzilla [1]. Quoting from it:
>
>> Hello,
>> 
>> I have a virtual machine running the old Windows Server 2003. On kernels 6.1.44 and 6.1.45, the QEMU VNC window stays dark, not switching to any of the guest's video modes and the VM process uses only ~64 MB of RAM of the assigned 2 GB, indefinitely. It's like the VM is paused/halted/stuck before even starting. The process can be killed successfully and then restarted again (with the same result), so it is not deadlocked in kernel or the like.
>> 
>> Kernel 6.1.43 works fine.
>> 
>> I have also tried downgrading CPU microcode from 20230808 to 20230719, but that did not help.
>> 
>> The CPU is AMD Ryzen 5900. I suspect some of the newly added mitigations may be the culprit?
>
> See Bugzilla for the full thread.
>
> Anyway, I'm adding it to regzbot as stable-specific regression:
>
> #regzbot introduced: v6.1.43..v6.1.44 https://bugzilla.kernel.org/show_bug.cgi?id=217799
> #regzbot title: Windows Server 2003 VM boot hang (only 64MB RAM allocated)
>
> Thanks.
>
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=217799

>From KVM's PoV, I don't see any KVM/x86 patches v6.1.44..v6.1.45 and in fact
there are only two x86 patches:

f2615bb47be4 x86/CPU/AMD: Do not leak quotient data after a division by 0
98cccbd0a19a x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction

and I'm pretty certain the later is unrelated; f2615bb47be4 looks like
it can, in theory, be related. Cc: Borislav.

-- 
Vitaly