linux-kernel - Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests

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Date:   Tue, 28 Feb 2023 20:24:12 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Takahiro Itazuri <itazur@...zon.com>
Cc:     dave.hansen@...ux.intel.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        pbonzini@...hat.com, seanjc@...gle.com, tglx@...utronix.de,
        x86@...nel.org, zulinx86@...il.com
Subject: Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests

On Tue, Feb 28, 2023 at 06:13:45PM +0000, Takahiro Itazuri wrote:
> VMMs trust to some extent that KVM_GET_SUPPORTED_CPUID returns cpuid
> information consistent with hardware, although they should not for some
> leaves (like CPU topoligy). IMHO, propagating these bits without VMM
> actions would be helpful since guests come to know IBRS related
> information of processors by default and applies mitigations properly
> based on that information.

I'd prefer if VMMs did supply whatever they prefer to the guests
instead. None of those bits are used in the kernel for mitigations, as
you've realized.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette