Re: [PATCH v12 01/45] KVM: guest_memfd: Optimize away conversion overheads via dead-code elimination

[Binbin Wu]

On 8/31/2026 8:25 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> 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.wu@xxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/1ec08cd8-3072-4753-ad5e-cd34956647f8@xxxxxxxxxxxxxxx
> Suggested-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>