[V1 PATCH 1/6] KVM: x86: Add support for testing private memory

[Vishal Annapurve]

Introduce HAVE_KVM_PRIVATE_MEM_TESTING config to be able to test fd based
approach to support private memory with non-confidential selftest VMs.
To support this testing few important aspects need to be considered from
the perspective of selftests -
* KVM needs to know whether the access from guest VM is private or shared.
Confidential VMs (SNP/TDX) carry a dedicated bit in gpa that can be used by
KVM to deduce the nature of the access.
Non-confidential VMs don't have mechanism to carry/convey such an
information to KVM. So KVM just relies on what attributes are set by
userspace VMM keeping the userspace VMM in the TCB for the testing
purposes.
* arch_private_mem_supported is updated to allow private memory logic to
work with non-confidential vm selftests.

Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c          | 4 ++++
 arch/x86/kvm/mmu/mmu_internal.h | 4 +++-
 virt/kvm/Kconfig                | 4 ++++
 virt/kvm/kvm_main.c             | 2 +-
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 10017a9f26ee..b3118d00b284 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4280,6 +4280,10 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 
 	fault->gfn = fault->addr >> PAGE_SHIFT;
 	fault->slot = kvm_vcpu_gfn_to_memslot(vcpu, fault->gfn);
+#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING
+	fault->is_private = kvm_slot_can_be_private(fault->slot) &&
+			kvm_mem_is_private(vcpu->kvm, fault->gfn);
+#endif
 
 	if (page_fault_handle_page_track(vcpu, fault))
 		return RET_PF_EMULATE;
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 5cdff5ca546c..2e759f39c2c5 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -188,7 +188,6 @@ struct kvm_page_fault {
 
 	/* Derived from mmu and global state.  */
 	const bool is_tdp;
-	const bool is_private;
 	const bool nx_huge_page_workaround_enabled;
 
 	/*
@@ -221,6 +220,9 @@ struct kvm_page_fault {
 	/* The memslot containing gfn. May be NULL. */
 	struct kvm_memory_slot *slot;
 
+	/* Derived from encryption bits of the faulting GPA for CVMs. */
+	bool is_private;
+
 	/* Outputs of kvm_faultin_pfn.  */
 	kvm_pfn_t pfn;
 	hva_t hva;
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 69ca59e82149..300876afb0ca 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -93,3 +93,7 @@ config HAVE_KVM_RESTRICTED_MEM
 config KVM_GENERIC_PRIVATE_MEM
        bool
        depends on HAVE_KVM_RESTRICTED_MEM
+
+config HAVE_KVM_PRIVATE_MEM_TESTING
+       bool
+       depends on KVM_GENERIC_PRIVATE_MEM
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index dae6a2c196ad..54e57b7f1c15 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1750,7 +1750,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
 
 bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
 {
-	return false;
+	return IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING);
 }
 
 static int check_memory_region_flags(struct kvm *kvm,
-- 
2.38.1.431.g37b22c650d-goog