linux-kernel - [RFC PATCH v3 33/59] KVM: x86/mmu: Ignore bits 63 and 62 when checking for "present" SPTEs

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Date:   Wed, 24 Nov 2021 16:20:16 -0800
From:   isaku.yamahata@...el.com
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [RFC PATCH v3 33/59] KVM: x86/mmu: Ignore bits 63 and 62 when checking for "present" SPTEs

From: Sean Christopherson <sean.j.christopherson@...el.com>

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@...el.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/kvm/mmu/paging_tmpl.h |  2 +-
 arch/x86/kvm/mmu/spte.h        | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 3a515c71e09c..80e821996728 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -1102,7 +1102,7 @@ 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 cc432f9a966b..56b6dd750fb1 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -208,6 +208,19 @@ static inline bool is_mmio_spte(u64 spte)
 	       likely(shadow_mmio_value);
 }
 
+static inline bool __is_shadow_present_pte(u64 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 !!(pte & SPTE_MMU_PRESENT_MASK);
-- 
2.25.1