linux-kernel - Re: [PATCH 04/10] KVM: x86/mmu: Add Suppress VE bit to EPT shadow_mmio_mask/shadow_present

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Date: Mon, 15 Apr 2024 21:07:45 +0800
From: Chao Gao <chao.gao@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, Isaku Yamahata
	<isaku.yamahata@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 04/10] KVM: x86/mmu: Add Suppress VE bit to EPT
 shadow_mmio_mask/shadow_present_mask

>+++ b/arch/x86/include/asm/vmx.h
>@@ -514,6 +514,7 @@ 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 6c7ab3aa6aa7..d97c4725c0b7 100644
>--- a/arch/x86/kvm/mmu/spte.c
>+++ b/arch/x86/kvm/mmu/spte.c
>@@ -413,7 +413,9 @@ 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;

This change makes !shadow_present_mask checks in FNAME(sync_spte) and
make_spte() pointless as shadow_present_mask will never be zero.

And the first sentence below in make_spte() also becomes stale. I suppose
this needs an update.

	/*
	 * For the EPT case, shadow_present_mask is 0 if hardware
	 * supports exec-only page table entries.  In that case,
	 * ACC_USER_MASK and shadow_user_mask are used to represent
	 * read access.  See FNAME(gpte_access) in paging_tmpl.h.
	 */


> 	/*
> 	 * EPT overrides the host MTRRs, and so KVM must program the desired
> 	 * memtype directly into the SPTEs.  Note, this mask is just the mask
>@@ -430,7 +432,7 @@ 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);
> 
>-- 
>2.43.0
>
>
>