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Date:   Fri, 15 Sep 2023 07:32:47 -0700
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Subject: Re: [PATCH 1/2] KVM: SVM: Fix TSC_AUX virtualization setup
From:   Sean Christopherson <seanjc@google.com>
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Babu Moger <babu.moger@amd.com>
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On Fri, Sep 15, 2023, Tom Lendacky wrote:
> On 9/14/23 16:13, Sean Christopherson wrote:
> This toggling possibility raises a question related to the second patch in
> this series that eliminates the use of the user return MSR for TSC_AUX.
> Depending on when the interfaces are called (set CPUID, host-initiated WRMSR
> of TSC_AUX, set CPUID again), I think we could end up in a state where the
> host TSC_AUX may not get restored properly, not 100% sure at the moment,
> though.

Give me a few minutes to respond to patch 2, I think it can be much simpler, more
performant, and avoid any races.

> Let me drop that patch from the series for now and just send the fix(es).
> I'll work through the other scenarios and code paths and send the user
> return MSR optimization as a separate series later.