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

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Message-ID: <Y/6FIeJ5KCOfKEPN@zn.tnic>
Date:   Tue, 28 Feb 2023 23:50:09 +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 10:24:16PM +0000, Takahiro Itazuri wrote:
> I'm still a kernel newbie and I don't have a strong opinion for that.
> I just thought it would be helpful if the KVM_GET_SUPPORTED_CPUID API
> returns the same security information as the host, as long as it is
> harmless.

Not harmless - cpufeatures.h should contain flags which the kernel uses
and not *every* CPUID bit out there.

If you want to advertize flags to guests, see
arch/x86/kvm/reverse_cpuid.h and the KVM-only feature flags. You can add
them there.

> https://documentation.suse.com/sles/15-SP1/html/SLES-all/cha-spectre.html

Well, I was against adding that to the documentation when I was at SUSE
but ...

-- 
Regards/Gruss,
    Boris.

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