Re: [PATCH v9 03/41] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined

[Xiaoyao Li]

On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote:
From: Sean Christopherson <sea...@google.com>

Though the patch order and diff of this patch is adjusted to what looks 
in v7, per Sean's request [1], the changelog still looks somewhat 
confusing and part incorrect to me.

[1] https://lore.kernel.org/all/akvgzoer1ytfk...@google.com/

Explicitly guard reporting support for KVM_MEMORY_ATTRIBUTE_PRIVATE based
on kvm_arch_has_private_mem being #defined in anticipation of decoupling
kvm_supported_mem_attributes() from CONFIG_KVM_VM_MEMORY_ATTRIBUTES.

As I commented in v8, the "in anticipation of" thing is not correct.

guest_memfd support for memory attributes will be unconditional to avoid
yet more macros (all architectures that support guest_memfd are expected to
use per-gmem attributes at some point), at which point enumerating support
KVM_MEMORY_ATTRIBUTE_PRIVATE based solely on memory attributes being
supported _somewhere_ would result in KVM over-reporting support on arm64.

1. I'm not sure what "memory attributes being supported somewhere" means.

2. the kvm_supported_mem_attributes() will be renamed to 
kvm_supported_vm_mem_attributes() and it's still under the guard of
CONFIG_KVM_VM_MEMORY_ATTRIBUTES, what's relationship with "guest_memfd 
support for memory attributes"?

Signed-off-by: Sean Christopherson <sea...@google.com>
Reviewed-by: Fuad Tabba <ta...@google.com>
Reviewed-by: Binbin Wu <binbin...@linux.intel.com>
Tested-by: Shivank Garg <shiva...@amd.com>
Signed-off-by: Ackerley Tng <ackerley...@google.com>
---
  include/linux/kvm_host.h | 2 +-
  virt/kvm/kvm_main.c      | 2 ++
  2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9f78a466c6f3e..c125d2e8155a7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -722,7 +722,7 @@ static inline int kvm_arch_vcpu_memslots_id(struct kvm_vcpu 
*vcpu)
  }
  #endif
  
-#ifndef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
+#ifndef kvm_arch_has_private_mem
  static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
  {
        return false;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 902aa166c9c0c..9501dd8d015d1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2421,8 +2421,10 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
  #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
  static u64 kvm_supported_mem_attributes(struct kvm *kvm)
  {
+#ifdef kvm_arch_has_private_mem
        if (!kvm || kvm_arch_has_private_mem(kvm))
                return KVM_MEMORY_ATTRIBUTE_PRIVATE;
+#endif
  
  	return 0;
  }