linux-kernel - [RFC PATCH v5 055/104] KVM: x86/tdp_mmu: prevent private/shared map based on PRIVATE

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Date:   Fri,  4 Mar 2022 11:49:11 -0800
From:   isaku.yamahata@...el.com
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [RFC PATCH v5 055/104] KVM: x86/tdp_mmu: prevent private/shared map based on PRIVATE_PROHIBIT

From: Isaku Yamahata <isaku.yamahata@...el.com>

Use the bit SPTE_PRIVATE_PROHIBIT in shared and private EPT to determine
which mapping, shared or private, is allowed.  If requested mapping isn't
allowed, return RET_PF_RETRY to wait for other vcpu to change it.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/kvm/mmu/spte.h    |  2 +-
 arch/x86/kvm/mmu/tdp_mmu.c | 22 +++++++++++++++++++---
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 25dffdb488d1..9c37381a6762 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -223,7 +223,7 @@ extern u64 __read_mostly shadow_init_value;
 
 static inline bool is_removed_spte(u64 spte)
 {
-	return spte == SHADOW_REMOVED_SPTE;
+	return (spte & ~SPTE_PRIVATE_PROHIBIT) == SHADOW_REMOVED_SPTE;
 }
 
 static inline bool is_private_prohibit_spte(u64 spte)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 6d750563824d..f6bd35831e32 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1038,9 +1038,25 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
 
 	WARN_ON(sp->role.level != fault->goal_level);
 
-	/* TDX shared GPAs are no executable, enforce this for the SDV. */
-	if (!kvm_is_private_gfn(vcpu->kvm, iter->gfn))
-		pte_access &= ~ACC_EXEC_MASK;
+	if (kvm_gfn_stolen_mask(vcpu->kvm)) {
+		if (is_private_spte(iter->sptep)) {
+			/*
+			 * This GPA is not allowed to map as private.  Let
+			 * vcpu loop in page fault until other vcpu change it
+			 * by MapGPA hypercall.
+			 */
+			if (fault->slot &&
+				is_private_prohibit_spte(iter->old_spte))
+				return RET_PF_RETRY;
+		} else {
+			/* This GPA is not allowed to map as shared. */
+			if (fault->slot &&
+				!is_private_prohibit_spte(iter->old_spte))
+				return RET_PF_RETRY;
+			/* TDX shared GPAs are no executable, enforce this. */
+			pte_access &= ~ACC_EXEC_MASK;
+		}
+	}
 
 	if (unlikely(!fault->slot))
 		new_spte = make_mmio_spte(vcpu,
-- 
2.25.1