linux-kernel - [PATCH v4 02/13] KVM: x86/mmu: Use kvm_ad_enabled() to determine if TDP MMU SPTEs need wrprot

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Message-ID: <20230321220021.2119033-3-seanjc@google.com>
Date:   Tue, 21 Mar 2023 15:00:10 -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,
        Vipin Sharma <vipinsh@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v4 02/13] KVM: x86/mmu: Use kvm_ad_enabled() to determine if
 TDP MMU SPTEs need wrprot

From: Vipin Sharma <vipinsh@...gle.com>

Use the constant-after-module-load kvm_ad_enabled() to check if SPTEs in
the TDP MMU need to be write-protected when clearing accessed/dirty status
instead of manually checking every SPTE.  The per-SPTE A/D enabling is
specific to nested EPT MMUs, i.e. when KVM is using EPT A/D bits but L1 is
not, and so cannot happen in the TDP MMU (which is non-nested only).

Keep the original code as sanity checks buried under MMU_WARN_ON().
MMU_WARN_ON() is more or less useless at the moment, but there are plans
to change that.

Link: https://lore.kernel.org/all/Yz4Qi7cn7TWTWQjj@google.com
Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
[sean: split to separate patch, apply to dirty path, write changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 7c25dbf32ecc..5a5642650c3e 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1621,7 +1621,10 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		if (!is_shadow_present_pte(iter.old_spte))
 			continue;
 
-		if (spte_ad_need_write_protect(iter.old_spte)) {
+		MMU_WARN_ON(kvm_ad_enabled() &&
+			    spte_ad_need_write_protect(iter.old_spte));
+
+		if (!kvm_ad_enabled()) {
 			if (is_writable_pte(iter.old_spte))
 				new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
 			else
@@ -1685,13 +1688,16 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
 		if (!mask)
 			break;
 
+		MMU_WARN_ON(kvm_ad_enabled() &&
+			    spte_ad_need_write_protect(iter.old_spte));
+
 		if (iter.level > PG_LEVEL_4K ||
 		    !(mask & (1UL << (iter.gfn - gfn))))
 			continue;
 
 		mask &= ~(1UL << (iter.gfn - gfn));
 
-		if (wrprot || spte_ad_need_write_protect(iter.old_spte)) {
+		if (wrprot || !kvm_ad_enabled()) {
 			if (is_writable_pte(iter.old_spte))
 				new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
 			else
-- 
2.40.0.rc2.332.ga46443480c-goog