Re: [PATCH v2 3/4] KVM: SVM: Prevent writes to TSC MSR when Secure TSC is enabled

[Sean Christopherson <seanjc@google.com>]

On Mon, Feb 10, 2025, Tom Lendacky wrote:
> On 2/10/25 03:22, Nikunj A Dadhania wrote:
> > Disallow writes to MSR_IA32_TSC for Secure TSC enabled SNP guests, as such
> > writes are not expected. Log the error and return #GP to the guest.
> 
> Re-word this to make it a bit clearer about why this is needed. It is
> expected that the guest won't write to MSR_IA32_TSC or, if it does, it
> will ignore any writes to it and not exit to the HV. So this is catching
> the case where that behavior is not occurring.

Unless it's architectural impossible for KVM to modify MSR_IA32_TSC, I don't see
any reason for KVM to care.  If the guest wants to modify TSC, that's the guest's
prerogative.

If KVM _can't_ honor the write, then that's something else entirely, and the
changelog should pretty much write itself.