linux-kernel - [RFC PATCH 3/9] KVM: x86/mmu: Set shadow_dirty

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Message-ID: <20240801183453.57199-4-seanjc@google.com>
Date: Thu,  1 Aug 2024 11:34:47 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 3/9] KVM: x86/mmu: Set shadow_dirty_mask for EPT even if
 A/D bits disabled

Set shadow_dirty_mask to the architectural EPT Dirty bit value even if
A/D bits are disabled at the module level, i.e. even if KVM will never
enable A/D bits in hardware.  Doing so provides consistent behavior for
Accessed and Dirty bits, i.e. doesn't leave KVM in a state where it sets
shadow_accessed_mask but not shadow_dirty_mask.

Functionally, this should be one big nop, as consumption of
shadow_dirty_mask is always guarded by a check that hardware A/D bits are
enabled.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/spte.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index cae45825617c..a0ff504f1e7e 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -441,7 +441,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
 
 	shadow_user_mask	= VMX_EPT_READABLE_MASK;
 	shadow_accessed_mask	= VMX_EPT_ACCESS_BIT;
-	shadow_dirty_mask	= has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
+	shadow_dirty_mask	= VMX_EPT_DIRTY_BIT;
 	shadow_nx_mask		= 0ull;
 	shadow_x_mask		= VMX_EPT_EXECUTABLE_MASK;
 	/* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
-- 
2.46.0.rc1.232.g9752f9e123-goog