linux-kernel - Re: [PATCH 0/3] Unify IBRS virtualization

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Message-ID: <Z9NMxr0Ri7VUlJzM@google.com>
Date: Thu, 13 Mar 2025 21:23:18 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: x86@...nel.org, Sean Christopherson <seanjc@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jim Mattson <jmattson@...gle.com>,
	"Kaplan, David" <David.Kaplan@....com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Unify IBRS virtualization

On Fri, Feb 21, 2025 at 04:33:49PM +0000, Yosry Ahmed wrote:
> To properly virtualize IBRS on Intel, an IBPB is executed on emulated
> VM-exits to provide separate predictor modes for L1 and L2.
> 
> Similar handling is theoretically needed for AMD, unless IbrsSameMode is
> enumerated by the CPU (which should be the case for most/all CPUs
> anyway). For correctness and clarity, this series generalizes the
> handling to apply for both Intel and AMD as needed.
> 
> I am not sure if this series would land through the kvm-x86 tree or the
> tip/x86 tree.

Sean, any thoughts about this (or general feedback about this series)?

> 
> Yosry Ahmed (3):
>   x86/cpufeatures: Define X86_FEATURE_AMD_IBRS_SAME_MODE
>   KVM: x86: Propagate AMD's IbrsSameMode to the guest
>   KVM: x86: Generalize IBRS virtualization on emulated VM-exit
> 
>  arch/x86/include/asm/cpufeatures.h       |  1 +
>  arch/x86/kvm/cpuid.c                     |  1 +
>  arch/x86/kvm/svm/nested.c                |  2 ++
>  arch/x86/kvm/vmx/nested.c                | 11 +----------
>  arch/x86/kvm/x86.h                       | 18 ++++++++++++++++++
>  tools/arch/x86/include/asm/cpufeatures.h |  1 +
>  6 files changed, 24 insertions(+), 10 deletions(-)
> 
> -- 
> 2.48.1.601.g30ceb7b040-goog
>