[PATCH v2] KVM: guest-memfd: fix unused-function warning

[PATCH v2] KVM: guest-memfd: fix unused-function warning

[Paolo Bonzini]

With migration disabled, one function becomes unused:

virt/kvm/guest_memfd.c:262:12: error: 'kvm_gmem_migrate_folio' defined but not used [-Werror=unused-function]
  262 | static int kvm_gmem_migrate_folio(struct address_space *mapping,
      |            ^~~~~~~~~~~~~~~~~~~~~~

Remove the #ifdef around the reference so that fallback_migrate_folio()
is never used.  The gmem implementation of the hook is trivial; since
the gmem mapping is unmovable, the pages should not be migrated anyway.

Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 virt/kvm/guest_memfd.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index b99272396119..c2e2371720a9 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -300,9 +300,7 @@ static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
 
 static const struct address_space_operations kvm_gmem_aops = {
 	.dirty_folio = noop_dirty_folio,
-#ifdef CONFIG_MIGRATION
 	.migrate_folio	= kvm_gmem_migrate_folio,
-#endif
 	.error_remove_page = kvm_gmem_error_page,
 };
 
-- 
2.39.1

Re: [PATCH v2] KVM: guest-memfd: fix unused-function warning

[Sean Christopherson]

On Fri, Dec 08, 2023, Paolo Bonzini wrote:
> With migration disabled, one function becomes unused:
> 
> virt/kvm/guest_memfd.c:262:12: error: 'kvm_gmem_migrate_folio' defined but not used [-Werror=unused-function]
>   262 | static int kvm_gmem_migrate_folio(struct address_space *mapping,
>       |            ^~~~~~~~~~~~~~~~~~~~~~
> 
> Remove the #ifdef around the reference so that fallback_migrate_folio()
> is never used.  The gmem implementation of the hook is trivial; since
> the gmem mapping is unmovable, the pages should not be migrated anyway.
> 
> Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>