On Fri, Jan 29, 2021, Paolo Bonzini wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 76bce832cade..15733013b266 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1401,7 +1401,7 @@ static u64 kvm_get_arch_capabilities(void)
> * This lets the guest use VERW to clear CPU buffers.
This comment be updated to call out the new TSX_CTRL behavior.
/*
* On TAA affected systems:
* - nothing to do if TSX is disabled on the host.
* - we emulate TSX_CTRL if present on the host.
* This lets the guest use VERW to clear CPU buffers.
*/
> */
> if (!boot_cpu_has(X86_FEATURE_RTM))
> - data &= ~(ARCH_CAP_TAA_NO | ARCH_CAP_TSX_CTRL_MSR);
> + data &= ~ARCH_CAP_TAA_NO;
Hmm, simply clearing TSX_CTRL will only preserve the host value. Since
ARCH_CAPABILITIES is unconditionally emulated by KVM, wouldn't it make sense to
unconditionally expose TSX_CTRL as well, as opposed to exposing it only if it's
supported in the host? I.e. allow migrating a TSX-disabled guest to a host
without TSX. Or am I misunderstanding how TSX_CTRL is checked/used?
> else if (!boot_cpu_has_bug(X86_BUG_TAA))
> data |= ARCH_CAP_TAA_NO;
>
> --
> 2.26.2
>
