KVM: guest_memfd: Explicitly pass number of pages to make_private() hook

Tweak the guest_memfd make_private() hook to explicitly pass the number of
pages to align with the signature of the make_shared() hook, and because
the existing code is outright broken if a guest_memfd folio is comprised of
more than one page (which can't happen, yet).  The SNP code *tries* to
create a corresponding huge entry, but if the RMP must use 4KiB entries for
whatever reason, KVM will only convert the first pfn, and not the entire
range of pfns that will be mapped into the guest.

Alternatively, @max_order could simply be repurposed as _the_ @order, but
that will fall apart when in-place conversion comes along, at which point
KVM will need to deal with conversions that aren't bound 1:1 to a folio.
I.e. the number of pages to convert may not be exactly a power-of-2 (and
folios don't strictly guarantee power-of-2 pages anyways).

WARN in the SNP code if the number of pages to prepare is anything other
than '1', i.e. if guest_memfd is trying to prepare/convert more than a
single 4KiB page, as sev_gmem_prepare() doesn't actually handle conversion
greater than order-0 folios.

Opportunistically swap the ordering of @pfn and @gfn params for
kvm_x86_ops.gmem_make_private() to match kvm_arch_gmem_make_private().

Fixes: b85524314a3d ("KVM: guest_memfd: delay kvm_gmem_prepare_folio() until the memory is passed to the guest")
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://patch.msgid.link/20260723210811.72720-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 6635ed05f411..0c1ee3e49176 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -77,7 +77,7 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo
 	kvm_pfn_t pfn = folio_file_pfn(folio, index);
 	gfn_t gfn = slot->base_gfn + index - slot->gmem.pgoff;
 
-	return kvm_arch_gmem_make_private(kvm, gfn, pfn, folio_order(folio));
+	return kvm_arch_gmem_make_private(kvm, gfn, pfn, folio_nr_pages(folio));
 #else
 	return 0;
 #endif