Re: [PATCH v10 035/108] KVM: x86/mmu: Track shadow MMIO value on a per-VM basis

Yan Zhao
2022-11-25T00:35:45Z

On Fri, Nov 25, 2022 at 08:13:48AM +0800, Huang, Kai wrote:
> On Tue, 2022-11-22 at 10:10 +0800, Yan Zhao wrote:
> > Also make enable_mmio_caching to be a per-VM value?
> > As if the shadow_mmio_value is 0, mmio_caching needs to be disabled.
>
> If I recall correctly, Sean said we can disable TDX guests if mmio_caching is
> disabled (we also will need to change to allow enable_mmio_caching to still be
> true when mmio_value is 0).
>
> SEV_ES has similar logic:
>
> void __init sev_hardware_setup(void)
> {
>
> ...
>
> /*
> * SEV-ES requires MMIO caching as KVM doesn't have access to the guest
> * instruction stream, i.e. can't emulate in response to a #NPF and
> * instead relies on #NPF(RSVD) being reflected into the guest as #VC
> * (the guest can then do a #VMGEXIT to request MMIO emulation).
> */
> if (!enable_mmio_caching)
> goto out;
>

Would enabling mmio caching in per-VM basis be better?