[PATCH RFC v9 04/51] KVM: x86: Determine shared/private faults using a configurable mask

[Michael Roth <michael.roth@xxxxxxx>]

This will be used to determine whether or not an #NPF should be serviced
using a normal page vs. a guarded/gmem one.

Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  7 +++++++
 arch/x86/kvm/mmu/mmu_internal.h | 35 ++++++++++++++++++++++++++++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b3bd24f2a390..c26f76641121 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1445,6 +1445,13 @@ struct kvm_arch {
 	 */
 #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
 	struct kvm_mmu_memory_cache split_desc_cache;
+
+	/*
+	 * When set, used to determine whether a fault should be treated as
+	 * private in the context of protected VMs which use a separate gmem
+	 * pool to back private guest pages.
+	 */
+	u64 mmu_private_fault_mask;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 780b91e1da9f..9b9e75aa43f4 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -252,6 +252,39 @@ 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)
+{
+	struct kvm_memory_slot *slot;
+	bool private_fault = false;
+	gfn_t gfn = gpa_to_gfn(gpa);
+
+	slot = gfn_to_memslot(kvm, gfn);
+	if (!slot) {
+		pr_debug("%s: no slot, GFN: 0x%llx\n", __func__, gfn);
+		goto out;
+	}
+
+	if (!kvm_slot_can_be_private(slot)) {
+		pr_debug("%s: slot is not private, GFN: 0x%llx\n", __func__, gfn);
+		goto out;
+	}
+
+	if (kvm->arch.mmu_private_fault_mask) {
+		private_fault = !!(err & kvm->arch.mmu_private_fault_mask);
+		goto out;
+	}
+
+	/*
+	 * Handling below is for UPM 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);
+
+out:
+	pr_debug("%s: GFN: 0x%llx, private: %d\n", __func__, gfn, private_fault);
+	return private_fault;
+}
+
 /*
  * Return values of handle_mmio_page_fault(), mmu.page_fault(), fast_page_fault(),
  * and of course kvm_mmu_do_page_fault().
@@ -301,7 +334,7 @@ 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