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

On Fri, Nov 11, 2022 at 01:42:39AM +0000, Vishal Annapurve wrote:

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@google.com

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;

Either we can wrap it with the CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING or if it looks ugly I can remove the "const" in my code.

Chao

• /* 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