linux-kernel - [PATCH RFC gmem v1 8/8] KVM: x86: Determine shared/private faults based on vm

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Message-ID: <20231016115028.996656-9-michael.roth@amd.com>
Date:   Mon, 16 Oct 2023 06:50:28 -0500
From:   Michael Roth <michael.roth@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <pbonzini@...hat.com>, <seanjc@...gle.com>,
        <isaku.yamahata@...el.com>, <ackerleytng@...gle.com>,
        <vbabka@...e.cz>, <ashish.kalra@....com>,
        <nikunj.dadhania@....com>, <jroedel@...e.de>,
        <pankaj.gupta@....com>
Subject: [PATCH RFC gmem v1 8/8] KVM: x86: Determine shared/private faults based on vm_type

For KVM_X86_SNP_VM, only the PFERR_GUEST_ENC_MASK flag is needed to
determine with an #NPF is due to a private/shared access by the guest.
Implement that handling here. Also add handling needed to deal with
SNP guests which in some cases will make MMIO accesses with the
encryption bit.

Signed-off-by: Michael Roth <michael.roth@....com>
---
 arch/x86/kvm/mmu/mmu.c          | 12 ++++++++++--
 arch/x86/kvm/mmu/mmu_internal.h | 20 +++++++++++++++++++-
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 686f88c263a9..10c323e2faa4 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4327,6 +4327,7 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
 static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_memory_slot *slot = fault->slot;
+	bool private_fault = fault->is_private;
 	bool async;
 
 	/*
@@ -4356,12 +4357,19 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 			return RET_PF_EMULATE;
 	}
 
-	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
+	/*
+	 * In some cases SNP guests will make MMIO accesses with the encryption
+	 * bit set. Handle these via the normal MMIO fault path.
+	 */
+	if (!slot && private_fault && kvm_is_vm_type(vcpu->kvm, KVM_X86_SNP_VM))
+		private_fault = false;
+
+	if (private_fault != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
 		kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
 		return -EFAULT;
 	}
 
-	if (fault->is_private)
+	if (private_fault)
 		return kvm_faultin_pfn_private(vcpu, fault);
 
 	async = false;
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 759c8b718201..e5b973051ad9 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -251,6 +251,24 @@ struct kvm_page_fault {
 
 int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
 
+static bool kvm_mmu_fault_is_private(struct kvm *kvm, gpa_t gpa, u64 err)
+{
+	bool private_fault = false;
+
+	if (kvm_is_vm_type(kvm, KVM_X86_SNP_VM)) {
+		private_fault = !!(err & PFERR_GUEST_ENC_MASK);
+	} else if (kvm_is_vm_type(kvm, KVM_X86_SW_PROTECTED_VM)) {
+		/*
+		 * This handling is for gmem self-tests and guests that treat
+		 * userspace as the authority on whether a fault should be
+		 * private or not.
+		 */
+		private_fault = kvm_mem_is_private(kvm, gpa >> PAGE_SHIFT);
+	}
+
+	return private_fault;
+}
+
 /*
  * Return values of handle_mmio_page_fault(), mmu.page_fault(), fast_page_fault(),
  * and of course kvm_mmu_do_page_fault().
@@ -298,7 +316,7 @@ 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),
+		.is_private = kvm_mmu_fault_is_private(vcpu->kvm, cr2_or_gpa, err),
 	};
 	int r;
 
-- 
2.25.1