linux-kernel - Re: [PATCH v8 23/30] KVM: selftests: Add functions to allow mapping as shared

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Message-ID: <d69b2da1-efc4-47da-a74d-c18d0b50db74@linux.intel.com>
Date: Fri, 15 Aug 2025 10:37:51 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sagi Shahar <sagis@...gle.com>
Cc: linux-kselftest@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
 Shuah Khan <shuah@...nel.org>, Sean Christopherson <seanjc@...gle.com>,
 Ackerley Tng <ackerleytng@...gle.com>, Ryan Afranji <afranji@...gle.com>,
 Andrew Jones <ajones@...tanamicro.com>,
 Isaku Yamahata <isaku.yamahata@...el.com>,
 Erdem Aktas <erdemaktas@...gle.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Roger Wang <runanwang@...gle.com>, Oliver Upton <oliver.upton@...ux.dev>,
 "Pratik R. Sampat" <pratikrajesh.sampat@....com>,
 Reinette Chatre <reinette.chatre@...el.com>, Ira Weiny
 <ira.weiny@...el.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 23/30] KVM: selftests: Add functions to allow mapping
 as shared

On 8/8/2025 4:16 AM, Sagi Shahar wrote:
> From: Ackerley Tng <ackerleytng@...gle.com>
>
> virt_map() enforces a private mapping for private memory. Introduce
> virt_map_shared() that creates a shared mapping for private as
> well as shared memory. This way, the TD does not have to remap its
> page tables at runtime.
>
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> Signed-off-by: Sagi Shahar <sagis@...gle.com>
> ---
>   .../testing/selftests/kvm/include/kvm_util.h  | 23 +++++++++++++
>   tools/testing/selftests/kvm/lib/kvm_util.c    | 34 +++++++++++++++++++
>   .../testing/selftests/kvm/lib/x86/processor.c | 15 ++++++--
>   3 files changed, 70 insertions(+), 2 deletions(-)
>
[...]
>   
> -void __virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr, int level)
> +static void ___virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr,
> +			   int level, bool protected)
>   {
>   	const uint64_t pg_size = PG_LEVEL_SIZE(level);
>   	uint64_t *pml4e, *pdpe, *pde;
> @@ -231,17 +232,27 @@ void __virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr, int level)
>   	 * Neither SEV nor TDX supports shared page tables, so only the final
>   	 * leaf PTE needs manually set the C/S-bit.
>   	 */
> -	if (vm_is_gpa_protected(vm, paddr))

Since the original code has already create shared/private mapping based on the
paddr, why not just use virt_map() and shared GPA as paddr, then no need to
duplicate the code?

> +	if (protected)
>   		*pte |= vm->arch.c_bit;
>   	else
>   		*pte |= vm->arch.s_bit;
>   }
>   
> +void __virt_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr, int level)
> +{
> +	___virt_pg_map(vm, vaddr, paddr, level, vm_is_gpa_protected(vm, paddr));
> +}
> +
>   void virt_arch_pg_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr)
>   {
>   	__virt_pg_map(vm, vaddr, paddr, PG_LEVEL_4K);
>   }
>   
> +void virt_arch_pg_map_shared(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr)
> +{
> +	___virt_pg_map(vm, vaddr, paddr, PG_LEVEL_4K, false);
> +}
> +
>   void virt_map_level(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr,
>   		    uint64_t nr_bytes, int level)
>   {