[RFC PATCH 37/67] KVM: x86/mmu: Ignore bits 63 and 62 when checking for "present" SPTEs

[isaku . yamahata]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

Ignore bits 63 and 62 when checking for present SPTEs to allow setting
said bits in not-present SPTEs.  TDX will set bit 63 in "zero" SPTEs to
suppress #VEs (TDX-SEAM unconditionally enables EPT Violation #VE), and
will use bit 62 to track zapped private SPTEs.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/mmu/paging_tmpl.h |  2 +-
 arch/x86/kvm/mmu/spte.h        | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 5d4e9f404018..06659d5c8ba0 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -1039,7 +1039,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 		gpa_t pte_gpa;
 		gfn_t gfn;
 
-		if (!sp->spt[i])
+		if (!__is_shadow_present_pte(sp->spt[i]))
 			continue;
 
 		pte_gpa = first_pte_gpa + i * sizeof(pt_element_t);
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index e5c94848ade1..22256cc8cce6 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -174,9 +174,22 @@ static inline bool is_access_track_spte(u64 spte)
 	return !spte_ad_enabled(spte) && (spte & shadow_acc_track_mask) == 0;
 }
 
-static inline int is_shadow_present_pte(u64 pte)
+static inline bool __is_shadow_present_pte(u64 pte)
 {
-	return (pte != 0) && !is_mmio_spte(pte);
+	/*
+	 * Ignore bits 63 and 62 so that they can be set in SPTEs that are well
+	 * and truly not present.  We can't use the sane/obvious approach of
+	 * querying bits 2:0 (RWX or P) because EPT without A/D bits will clear
+	 * RWX of a "present" SPTE to do access tracking.  Tracking updates can
+	 * be done out of mmu_lock, so even the flushing logic needs to treat
+	 * such SPTEs as present.
+	 */
+	return !!(pte << 2);
+}
+
+static inline bool is_shadow_present_pte(u64 pte)
+{
+	return __is_shadow_present_pte(pte) && !is_mmio_spte(pte);
 }
 
 static inline int is_large_pte(u64 pte)
-- 
2.17.1