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

[Chao Peng]

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@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;

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