linux-kernel - [V2 PATCH 1/6] KVM: x86: Add support for testing private memory

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Date:   Mon,  5 Dec 2022 23:23:36 +0000
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     pbonzini@...hat.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, shuah@...nel.org, yang.zhong@...el.com,
        ricarkol@...gle.com, aaronlewis@...gle.com, wei.w.wang@...el.com,
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        dmatlack@...gle.com, axelrasmussen@...gle.com,
        maciej.szmigiero@...cle.com, mizhang@...gle.com,
        bgardon@...gle.com, ackerleytng@...gle.com,
        Vishal Annapurve <vannapurve@...gle.com>
Subject: [V2 PATCH 1/6] KVM: x86: Add support for testing private memory

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@...gle.com>
---
 arch/x86/kvm/mmu/mmu_internal.h | 6 +++++-
 virt/kvm/Kconfig                | 4 ++++
 virt/kvm/kvm_main.c             | 3 ++-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 5ccf08183b00..e2f508db0b6e 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -263,6 +263,8 @@ enum {
 static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 					u32 err, bool prefetch)
 {
+	bool is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault);
+
 	struct kvm_page_fault fault = {
 		.addr = cr2_or_gpa,
 		.error_code = err,
@@ -272,13 +274,15 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		.rsvd = err & PFERR_RSVD_MASK,
 		.user = err & PFERR_USER_MASK,
 		.prefetch = prefetch,
-		.is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
+		.is_tdp = is_tdp,
 		.nx_huge_page_workaround_enabled =
 			is_nx_huge_page_enabled(vcpu->kvm),
 
 		.max_level = KVM_MAX_HUGEPAGE_LEVEL,
 		.req_level = PG_LEVEL_4K,
 		.goal_level = PG_LEVEL_4K,
+		.is_private = IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING) && is_tdp &&
+				kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
 	};
 	int r;
 
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index d605545d6dd1..1e326367a21c 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -92,3 +92,7 @@ config HAVE_KVM_PM_NOTIFIER
 
 config HAVE_KVM_RESTRICTED_MEM
        bool
+
+config HAVE_KVM_PRIVATE_MEM_TESTING
+       bool "Private memory selftests"
+       depends on HAVE_KVM_MEMORY_ATTRIBUTES && HAVE_KVM_RESTRICTED_MEM
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ac835fc77273..d2d829d23442 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1262,7 +1262,8 @@ int __weak kvm_arch_create_vm_debugfs(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 struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
-- 
2.39.0.rc0.267.gcb52ba06e7-goog