linux-kernel - Re: [PATCH 05/21] KVM: x86/mmu: Add Suppress VE bit to EPT shadow_mmio_mask/shadow_present

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Date: Fri, 1 Mar 2024 15:26:05 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: seanjc@...gle.com, michael.roth@....com, isaku.yamahata@...el.com,
 thomas.lendacky@....com
Subject: Re: [PATCH 05/21] KVM: x86/mmu: Add Suppress VE bit to EPT
 shadow_mmio_mask/shadow_present_mask

On 2/28/2024 7:20 AM, Paolo Bonzini wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> To make use of the same value of shadow_mmio_mask and shadow_present_mask
> for TDX and VMX, add Suppress-VE bit to shadow_mmio_mask and
> shadow_present_mask so that they can be common for both VMX and TDX.
> 
> TDX will require shadow_mmio_mask and shadow_present_mask to include
> VMX_SUPPRESS_VE for shared GPA so that EPT violation is triggered for
> shared GPA.  For VMX, VMX_SUPPRESS_VE doesn't matter for MMIO because the
> spte value is defined so as to cause EPT misconfig.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Message-Id: <97cc616b3563cd8277be91aaeb3e14bce23c3649.1705965635.git.isaku.yamahata@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> ---
>   arch/x86/include/asm/vmx.h | 1 +
>   arch/x86/kvm/mmu/spte.c    | 6 ++++--
>   2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index 0e73616b82f3..76ed39541a52 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -513,6 +513,7 @@ enum vmcs_field {
>   #define VMX_EPT_IPAT_BIT    			(1ull << 6)
>   #define VMX_EPT_ACCESS_BIT			(1ull << 8)
>   #define VMX_EPT_DIRTY_BIT			(1ull << 9)
> +#define VMX_EPT_SUPPRESS_VE_BIT			(1ull << 63)
>   #define VMX_EPT_RWX_MASK                        (VMX_EPT_READABLE_MASK |       \
>   						 VMX_EPT_WRITABLE_MASK |       \
>   						 VMX_EPT_EXECUTABLE_MASK)
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 4a599130e9c9..02a466de2991 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -429,7 +429,9 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
>   	shadow_dirty_mask	= has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
>   	shadow_nx_mask		= 0ull;
>   	shadow_x_mask		= VMX_EPT_EXECUTABLE_MASK;
> -	shadow_present_mask	= has_exec_only ? 0ull : VMX_EPT_READABLE_MASK;
> +	/* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
> +	shadow_present_mask	=
> +		(has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT;
>   	/*
>   	 * EPT overrides the host MTRRs, and so KVM must program the desired
>   	 * memtype directly into the SPTEs.  Note, this mask is just the mask
> @@ -446,7 +448,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
>   	 * of an EPT paging-structure entry is 110b (write/execute).
>   	 */
>   	kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
> -				   VMX_EPT_RWX_MASK, 0);
> +				   VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
>   }
>   EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
>