Re: [PATCH v13 01/44] KVM: guest_memfd: Optimize away conversion overheads via dead-code elimination

[Xiaoyao Li]

On 9/11/2026 7:55 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <sea...@google.com>
> 
> Add and use kvm_arch_has_gmem_convert() to guard guest_memfd's invocation
> of arch hooks related to converting memory between private and shared, as
> only one half of the x86 CoCo duo needs the runtime hooks (any pre-work is
> pure overhead for TDX).  At this exact moment, the overhead is negligible,
> but that will change when in-place conversion comes along, at which point
> to-shared conversions will "need" to find all affected folios prior to
> calling into arch code.  In quotes because very technically that work could
> be pushed to arch code, but that would bleed guest_memfd details into arch
> code and would be far worse than adding yet another kvm_arch_has... hook.
> 
> Opportunistically provide the kvm_arch_gmem_make_private() declaration, and
> rely on dead-code elimination to eliminate the call to non-existent code
> when CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT=n.
> 
> Reported-by: Binbin Wu <binbin...@linux.intel.com>
> Closes: 
> https://lore.kernel.org/all/1ec08cd8-3072-4753-ad5e-cd3495664...@linux.intel.com
> Suggested-by: Ackerley Tng <ackerley...@google.com>
> Signed-off-by: Sean Christopherson <sea...@google.com>
> Signed-off-by: Ackerley Tng <ackerley...@google.com>
> Reviewed-by: Fuad Tabba <fuad.ta...@linux.dev>
> Reviewed-by: Binbin Wu <binbin...@linux.intel.com>
> Reviewed-by: David Hildenbrand (Arm) <da...@kernel.org>
Reviewed-by: Xiaoyao Li <xiaoyao...@intel.com>