Date:   Mon, 27 Feb 2023 22:40:21 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Takahiro Itazuri <itazur@amazon.com>
Cc:     kvm@vger.kernel.org, x86@kernel.org,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org, Takahiro Itazuri <zulinx86@gmail.com>
Subject: Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests
Message-ID: <Y/0jRXzbcbxTjqSS@zn.tnic>
References: <20230227210526.83182-1-itazur@amazon.com>
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On Mon, Feb 27, 2023 at 09:05:24PM +0000, Takahiro Itazuri wrote:
> VMMs retrieve supported CPUID features via KVM_GET_SUPPORTED_CPUID to
> construct CPUID information to be passed to KVM_SET_CPUID2. Most CPUID
> feature bits related to speculative attacks are propagated from host
> CPUID. But AMD processors have AMD-specific IBRS related bits in CPUID
> Fn8000_0008_EBX (ref: AMD64 Architecture Programmer's Manual Volume 3:
> General-Purpose and System Instructions) and some bits are not
> propagated to guests.
> 
> Enable propagation of these bits to guests, so that VMMs don't have to
> enable them explicitly based on host CPUID.

How hard is it for the VMMs to enable them?

-- 
Regards/Gruss,
    Boris.

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