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SubjectRe: [PATCH v2 46/46] KVM: x86: Preserve guest's CR0.CD/NW on INIT
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> On Jul 19, 2021, at 9:37 PM, Reiji Watanabe <reijiw@google.com> wrote:
>
> On Tue, Jul 13, 2021 at 9:35 AM Sean Christopherson <seanjc@google.com> wrote:
>>
>> Preserve CR0.CD and CR0.NW on INIT instead of forcing them to '1', as
>> defined by both Intel's SDM and AMD's APM.
>>
>> Note, current versions of Intel's SDM are very poorly written with
>> respect to INIT behavior. Table 9-1. "IA-32 and Intel 64 Processor
>> States Following Power-up, Reset, or INIT" quite clearly lists power-up,
>> RESET, _and_ INIT as setting CR0=60000010H, i.e. CD/NW=1. But the SDM
>> then attempts to qualify CD/NW behavior in a footnote:
>>
>> 2. The CD and NW flags are unchanged, bit 4 is set to 1, all other bits
>> are cleared.
>>
>> Presumably that footnote is only meant for INIT, as the RESET case and
>> especially the power-up case are rather non-sensical. Another footnote
>> all but confirms that:
>>
>> 6. Internal caches are invalid after power-up and RESET, but left
>> unchanged with an INIT.
>>
>> Bare metal testing shows that CD/NW are indeed preserved on INIT (someone
>> else can hack their BIOS to check RESET and power-up :-D).
>>
>> Reported-by: Reiji Watanabe <reijiw@google.com>
>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>
> Reviewed-by: Reiji Watanabe <reijiw@google.com>
>
> Thank you for the fix and checking the CD/NW with the bare metal testing.

Interesting.

Is there a kvm-unit-test to reproduce the issue by any chance?

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