Re: [PATCH v14 03/21] KVM: Introduce kvm_arch_supports_gmem()

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 7/15/2025 5:33 PM, Fuad Tabba wrote:
> Introduce kvm_arch_supports_gmem() to explicitly indicate whether an
> architecture supports guest_memfd.
> 
> Previously, kvm_arch_has_private_mem() was used to check for guest_memfd
> support. However, this conflated guest_memfd with "private" memory,
> implying that guest_memfd was exclusively for CoCo VMs or other private
> memory use cases.
> 
> With the expansion of guest_memfd to support non-private memory, such as
> shared host mappings, it is necessary to decouple these concepts. The
> new kvm_arch_supports_gmem() function provides a clear way to check for
> guest_memfd support.
> 
> 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 +++-
>   include/linux/kvm_host.h        | 11 +++++++++++
>   virt/kvm/kvm_main.c             |  4 ++--
>   3 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index acb25f935d84..bde811b2d303 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -2277,8 +2277,10 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
>   
>   #ifdef CONFIG_KVM_GMEM
>   #define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
> +#define kvm_arch_supports_gmem(kvm) kvm_arch_has_private_mem(kvm)
>   #else
>   #define kvm_arch_has_private_mem(kvm) false
> +#define kvm_arch_supports_gmem(kvm) false
>   #endif
>   
>   #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)
> @@ -2331,7 +2333,7 @@ enum {
>   #define HF_SMM_INSIDE_NMI_MASK	(1 << 2)
>   
>   # define KVM_MAX_NR_ADDRESS_SPACES	2
> -/* SMM is currently unsupported for guests with private memory. */
> +/* SMM is currently unsupported for guests with guest_memfd private memory. */

Please don't change the comment.

As below, it checks kvm_arch_has_private_mem(). Nothing to do with 
guest_memfd.

Otherwise,

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>

>   # define kvm_arch_nr_memslot_as_ids(kvm) (kvm_arch_has_private_mem(kvm) ? 1 : 2)
>   # define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? 1 : 0)
>   # define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm)