KVM: remove kvm_arch_gmem_prepare_needed()

JIRA: https://issues.redhat.com/browse/RHEL-32435

It is enough to return 0 if a guest need not do any preparation.
This is in fact how sev_gmem_prepare() works for non-SNP guests,
and it extends naturally to Intel hosts: the x86 callback for
gmem_prepare is optional and returns 0 if not defined.

Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 7239ed7)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: bonzini

arch/x86/kvm/x86.c

@@ -13616,11 +13616,6 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
 EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
 
 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
-bool kvm_arch_gmem_prepare_needed(struct kvm *kvm)
-{
-	return kvm->arch.vm_type == KVM_X86_SNP_VM;
-}
-
 int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order)
 {
 	return static_call(kvm_x86_gmem_prepare)(kvm, pfn, gfn, max_order);

include/linux/kvm_host.h

@@ -2445,7 +2445,6 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
 
 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
 int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order);
-bool kvm_arch_gmem_prepare_needed(struct kvm *kvm);
 #endif
 
 /**

virt/kvm/guest_memfd.c

@@ -29,16 +29,9 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo
 				    pgoff_t index, struct folio *folio)
 {
 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
-	kvm_pfn_t pfn;
-	gfn_t gfn;
-	int rc;
-
-	if (!kvm_arch_gmem_prepare_needed(kvm))
-		return 0;
-
-	pfn = folio_file_pfn(folio, index);
-	gfn = slot->base_gfn + index - slot->gmem.pgoff;
-	rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
+	kvm_pfn_t pfn = folio_file_pfn(folio, index);
+	gfn_t gfn = slot->base_gfn + index - slot->gmem.pgoff;
+	int rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
 	if (rc) {
 		pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
 				    index, gfn, pfn, rc);