From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: Re: FYI: xapic_state_test selftest fails with avic enabled
Date: Tue, 23 Aug 2022 14:19:05 +0000 [thread overview]
Message-ID: <YwTh2b8ThbiEA7iq@google.com> (raw)
In-Reply-To: <cdbe3d8d07557d73d7a96cd4a69e717574494e34.camel@redhat.com>
On Tue, Aug 23, 2022, Maxim Levitsky wrote:
> Hi!
>
> I just noticed that this test fails when the AVIC is enabled.
>
> It seems that it exposes actual shortcomings in the AVIC hardware implementation,
> although these should not matter in real life usage of it.
>
>
> First of all it seems that AVIC just allows to set the APIC_ICR_BUSY bit (it should be read-only)
> and it never clears it if set.
>
> Second AVIC seems to drop writes to low 24 bits of to ICR2, because these are not really used,
> although technically not marked as reserved in the spec (though APIC_ID register in AMD spec,
> states explicity that only bits 24-31 can be set, and the rest are reserved).
>
> And finally AVIC inhibit when x2apic is exposed to the guest was recently removed,
> because in this case AVIC also works just fine (but with msr emulation) and that
> means that we don't need anymore to hide x2apic from the guest to avoid AVIC inhibit.
KUT's APIC test also fails for a variety of reasons when AVIC is enabled.
https://lore.kernel.org/all/20220204214410.3315068-1-seanjc@google.com
prev parent reply other threads:[~2022-08-23 16:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-23 12:57 FYI: xapic_state_test selftest fails with avic enabled Maxim Levitsky
2022-08-23 14:19 ` Sean Christopherson [this message]
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