Re: [PATCH v12 04/18] KVM: x86: Rename kvm->arch.has_private_mem to kvm->arch.supports_gmem

[Sean Christopherson <seanjc@google.com>]

On Wed, Jun 11, 2025, Fuad Tabba wrote:
> The bool has_private_mem is used to indicate whether guest_memfd is
> supported.

No?  This is at best weird, and at worst flat out wrong:

	if (kvm->arch.supports_gmem &&
	    fault->is_private != kvm_mem_is_private(kvm, fault->gfn))
		return false;

ditto for this code:

	if (kvm_arch_supports_gmem(vcpu->kvm) &&
	    kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa)))i
		error_code |= PFERR_PRIVATE_ACCESS;

and for the memory_attributes code.  E.g. IIRC, with guest_memfd() mmap support,
private vs. shared will become a property of the guest_memfd inode, i.e. this will
become wrong:

static u64 kvm_supported_mem_attributes(struct kvm *kvm)
{
	if (!kvm || kvm_arch_supports_gmem(kvm))
		return KVM_MEMORY_ATTRIBUTE_PRIVATE;

	return 0;
}

Instead of renaming kvm_arch_has_private_mem() => kvm_arch_supports_gmem(), *add*
kvm_arch_supports_gmem() and then kill off kvm_arch_has_private_mem() once non-x86
usage is gone (i.e. query kvm->arch.has_private_mem directly).

And then rather than rename has_private_mem, either add supports_gmem or do what
you did for kvm_arch_supports_gmem_shared_mem() and explicitly check the VM type.

> Rename it to supports_gmem to make its meaning clearer and to decouple memory
> being private from guest_memfd.
> 
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: Shivank Garg <shivankg@amd.com>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> Co-developed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 4 ++--
>  arch/x86/kvm/mmu/mmu.c          | 2 +-
>  arch/x86/kvm/svm/svm.c          | 4 ++--
>  arch/x86/kvm/x86.c              | 3 +--
>  4 files changed, 6 insertions(+), 7 deletions(-)

This missed the usage in TDX (it's not a staleness problem, because this series
was based on 6.16-rc1, which has the relevant code).

arch/x86/kvm/vmx/tdx.c: In function ‘tdx_vm_init’:
arch/x86/kvm/vmx/tdx.c:627:18: error: ‘struct kvm_arch’ has no member named ‘has_private_mem’
  627 |         kvm->arch.has_private_mem = true;
      |                  ^
make[5]: *** [scripts/Makefile.build:287: arch/x86/kvm/vmx/tdx.o] Error 1