linux-kernel - [PATCH 01/12] KVM: x86/mmu: Don't treat fully writable SPTEs as volatile (modulo A/D)

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Message-Id: <20220423034752.1161007-2-seanjc@google.com>
Date:   Sat, 23 Apr 2022 03:47:41 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: [PATCH 01/12] KVM: x86/mmu: Don't treat fully writable SPTEs as
 volatile (modulo A/D)

Don't treat SPTEs that are truly writable, i.e. writable in hardware, as
being volatile (unless they're volatile for other reasons, e.g. A/D bits).
KVM _sets_ the WRITABLE bit out of mmu_lock, but never _clears_ the bit
out of mmu_lock, so if the WRITABLE bit is set, it cannot magically get
cleared just because the SPTE is MMU-writable.

Rename the wrapper of MMU-writable to be more literal, the previous name
of spte_can_locklessly_be_made_writable() is wrong and misleading.

Fixes: c7ba5b48cc8d ("KVM: MMU: fast path of handling guest page fault")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c  | 17 +++++++++--------
 arch/x86/kvm/mmu/spte.h |  2 +-
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 904f0faff218..612316768e8e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -481,13 +481,15 @@ static bool spte_has_volatile_bits(u64 spte)
 	 * also, it can help us to get a stable is_writable_pte()
 	 * to ensure tlb flush is not missed.
 	 */
-	if (spte_can_locklessly_be_made_writable(spte) ||
-	    is_access_track_spte(spte))
+	if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
+		return true;
+
+	if (is_access_track_spte(spte))
 		return true;
 
 	if (spte_ad_enabled(spte)) {
-		if ((spte & shadow_accessed_mask) == 0 ||
-	    	    (is_writable_pte(spte) && (spte & shadow_dirty_mask) == 0))
+		if (!(spte & shadow_accessed_mask) ||
+		    (is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
 			return true;
 	}
 
@@ -554,7 +556,7 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
 	 * we always atomically update it, see the comments in
 	 * spte_has_volatile_bits().
 	 */
-	if (spte_can_locklessly_be_made_writable(old_spte) &&
+	if (is_mmu_writable_spte(old_spte) &&
 	      !is_writable_pte(new_spte))
 		flush = true;
 
@@ -1192,7 +1194,7 @@ static bool spte_write_protect(u64 *sptep, bool pt_protect)
 	u64 spte = *sptep;
 
 	if (!is_writable_pte(spte) &&
-	      !(pt_protect && spte_can_locklessly_be_made_writable(spte)))
+	    !(pt_protect && is_mmu_writable_spte(spte)))
 		return false;
 
 	rmap_printk("spte %p %llx\n", sptep, *sptep);
@@ -3171,8 +3173,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		 * be removed in the fast path only if the SPTE was
 		 * write-protected for dirty-logging or access tracking.
 		 */
-		if (fault->write &&
-		    spte_can_locklessly_be_made_writable(spte)) {
+		if (fault->write && is_mmu_writable_spte(spte)) {
 			new_spte |= PT_WRITABLE_MASK;
 
 			/*
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index ad8ce3c5d083..570699682f6d 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -398,7 +398,7 @@ static inline void check_spte_writable_invariants(u64 spte)
 			  "kvm: Writable SPTE is not MMU-writable: %llx", spte);
 }
 
-static inline bool spte_can_locklessly_be_made_writable(u64 spte)
+static inline bool is_mmu_writable_spte(u64 spte)
 {
 	return spte & shadow_mmu_writable_mask;
 }
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog