linux-kernel - [PATCH 01/24] KVM: x86/mmu: Set SPTE_AD_WRPROT_ONLY

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Date:   Thu, 25 Feb 2021 12:47:26 -0800
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>
Subject: [PATCH 01/24] KVM: x86/mmu: Set SPTE_AD_WRPROT_ONLY_MASK if and only
 if PML is enabled

Check that PML is actually enabled before setting the mask to force a
SPTE to be write-protected.  The bits used for the !AD_ENABLED case are
in the upper half of the SPTE.  With 64-bit paging and EPT, these bits
are ignored, but with 32-bit PAE paging they are reserved.  Setting them
for L2 SPTEs without checking PML breaks NPT on 32-bit KVM.

Fixes: 1f4e5fc83a42 ("KVM: x86: fix nested guest live migration with PML")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu_internal.h | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 72b0928f2b2d..ec4fc28b325a 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -81,15 +81,15 @@ static inline struct kvm_mmu_page *sptep_to_sp(u64 *sptep)
 static inline bool kvm_vcpu_ad_need_write_protect(struct kvm_vcpu *vcpu)
 {
 	/*
-	 * When using the EPT page-modification log, the GPAs in the log
-	 * would come from L2 rather than L1.  Therefore, we need to rely
-	 * on write protection to record dirty pages.  This also bypasses
-	 * PML, since writes now result in a vmexit.  Note, this helper will
-	 * tag SPTEs as needing write-protection even if PML is disabled or
-	 * unsupported, but that's ok because the tag is consumed if and only
-	 * if PML is enabled.  Omit the PML check to save a few uops.
+	 * When using the EPT page-modification log, the GPAs in the CPU dirty
+	 * log would come from L2 rather than L1.  Therefore, we need to rely
+	 * on write protection to record dirty pages, which bypasses PML, since
+	 * writes now result in a vmexit.  Note, the check on CPU dirty logging
+	 * being enabled is mandatory as the bits used to denote WP-only SPTEs
+	 * are reserved for NPT w/ PAE (32-bit KVM).
 	 */
-	return vcpu->arch.mmu == &vcpu->arch.guest_mmu;
+	return vcpu->arch.mmu == &vcpu->arch.guest_mmu &&
+	       kvm_x86_ops.cpu_dirty_log_size;
 }
 
 bool is_nx_huge_page_enabled(void);
-- 
2.30.1.766.gb4fecdf3b7-goog