linux-kernel - [PATCH v2 09/10] KVM: x86/mmu: Use PFERR_GUEST_ENC

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Date: Tue, 16 Apr 2024 16:19:34 -0400
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: isaku.yamahata@...el.com,
	xiaoyao.li@...el.com,
	binbin.wu@...ux.intel.com,
	chao.gao@...el.com
Subject: [PATCH v2 09/10] KVM: x86/mmu: Use PFERR_GUEST_ENC_MASK to indicate fault is private

SEV-SNP defines PFERR_GUEST_ENC_MASK (bit 34) in page-fault error bits to
represent the guest page is encrypted.  Use the bit to designate that the
page fault is private and that it requires looking up memory attributes.

The vendor kvm page fault handler should set PFERR_GUEST_ENC_MASK bit based
on their fault information.  It may or may not use the hardware value
directly or parse the hardware value to set the bit.

Based on a patch by Isaku Yamahata.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/include/asm/kvm_host.h | 2 ++
 arch/x86/kvm/mmu/mmu.c          | 9 +++++++++
 arch/x86/kvm/mmu/mmu_internal.h | 2 +-
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9f92bdb78504..7c73952b6f4e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -264,6 +264,7 @@ enum x86_intercept_stage;
 #define PFERR_SGX_BIT 15
 #define PFERR_GUEST_FINAL_BIT 32
 #define PFERR_GUEST_PAGE_BIT 33
+#define PFERR_GUEST_ENC_BIT 34
 #define PFERR_IMPLICIT_ACCESS_BIT 48
 
 #define PFERR_PRESENT_MASK	BIT(PFERR_PRESENT_BIT)
@@ -275,6 +276,7 @@ enum x86_intercept_stage;
 #define PFERR_SGX_MASK		BIT(PFERR_SGX_BIT)
 #define PFERR_GUEST_FINAL_MASK	BIT_ULL(PFERR_GUEST_FINAL_BIT)
 #define PFERR_GUEST_PAGE_MASK	BIT_ULL(PFERR_GUEST_PAGE_BIT)
+#define PFERR_GUEST_ENC_MASK	BIT_ULL(PFERR_GUEST_ENC_BIT)
 #define PFERR_IMPLICIT_ACCESS	BIT_ULL(PFERR_IMPLICIT_ACCESS_BIT)
 
 #define PFERR_NESTED_GUEST_PAGE (PFERR_GUEST_PAGE_MASK |	\
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 00eef18ca1ae..33aea47dce8b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5793,6 +5793,7 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 {
 	int r, emulation_type = EMULTYPE_PF;
 	bool direct = vcpu->arch.mmu->root_role.direct;
+	struct kvm *kvm = vcpu->kvm;
 
 	/*
 	 * IMPLICIT_ACCESS is a KVM-defined flag used to correctly perform SMAP
@@ -5808,6 +5809,14 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 	if (WARN_ON_ONCE(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
 		return RET_PF_RETRY;
 
+	/*
+	 * There is no vendor code that can set PFERR_GUEST_ENC_MASK for
+	 * software-protected VMs.  Compute it here.
+	 */
+	if (kvm->arch.vm_type == KVM_X86_SW_PROTECTED_VM &&
+	    kvm_mem_is_private(kvm, cr2_or_gpa >> PAGE_SHIFT))
+		error_code |= PFERR_GUEST_ENC_MASK;
+
 	r = RET_PF_INVALID;
 	if (unlikely(error_code & PFERR_RSVD_MASK)) {
 		r = handle_mmio_page_fault(vcpu, cr2_or_gpa, direct);
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 49b428cca04e..7c2ba50cec68 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -290,6 +290,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		.present = err & PFERR_PRESENT_MASK,
 		.rsvd = err & PFERR_RSVD_MASK,
 		.user = err & PFERR_USER_MASK,
+		.is_private = vcpu->kvm->arch.has_private_mem && (err & PFERR_GUEST_ENC_MASK),
 		.prefetch = prefetch,
 		.is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
 		.nx_huge_page_workaround_enabled =
@@ -298,7 +299,6 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		.max_level = KVM_MAX_HUGEPAGE_LEVEL,
 		.req_level = PG_LEVEL_4K,
 		.goal_level = PG_LEVEL_4K,
-		.is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
 	};
 	int r;
 
-- 
2.43.0