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

[Huang, Kai]

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;