Re: [PATCH 12/21] KVM: TDX: Set per-VM shadow_mmio_value to 0

[Paolo Bonzini]

On 9/4/24 05:07, Rick Edgecombe wrote:
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 46a26be0245b..4ab6d2a87032 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -94,8 +94,6 @@ u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access)
>   	u64 spte = generation_mmio_spte_mask(gen);
>   	u64 gpa = gfn << PAGE_SHIFT;
>   
> -	WARN_ON_ONCE(!vcpu->kvm->arch.shadow_mmio_value);
> -
>   	access &= shadow_mmio_access_mask;
>   	spte |= vcpu->kvm->arch.shadow_mmio_value | access;
>   	spte |= gpa | shadow_nonpresent_or_rsvd_mask;
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 0c08062ef99f..9da71782660f 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -6,7 +6,7 @@
>   #include "mmu.h"
>   #include "tdx.h"
>   #include "tdx_ops.h"
> -
> +#include "mmu/spte.h"
>   
>   #undef pr_fmt
>   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> @@ -344,6 +344,19 @@ int tdx_vm_init(struct kvm *kvm)
>   {
>   	kvm->arch.has_private_mem = true;
>   
> +	/*
> +	 * Because guest TD is protected, VMM can't parse the instruction in TD.
> +	 * Instead, guest uses MMIO hypercall.  For unmodified device driver,
> +	 * #VE needs to be injected for MMIO and #VE handler in TD converts MMIO
> +	 * instruction into MMIO hypercall.
> +	 *
> +	 * SPTE value for MMIO needs to be setup so that #VE is injected into
> +	 * TD instead of triggering EPT MISCONFIG.
> +	 * - RWX=0 so that EPT violation is triggered.
> +	 * - suppress #VE bit is cleared to inject #VE.
> +	 */
> +	kvm_mmu_set_mmio_spte_value(kvm, 0);
> +
>   	/*
>   	 * This function initializes only KVM software construct.  It doesn't
>   	 * initialize TDX stuff, e.g. TDCS, TDR, TDCX, HKID etc.

Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>