KVM: SVM: Fix an error code in sev_gmem_post_populate()

The copy_from_user() function returns the number of bytes which it
was not able to copy.  Return -EFAULT instead.

Fixes: dee5a47c ("KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Message-ID: <20240612115040.2423290-4-dan.carpenter@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -2290,9 +2290,10 @@ static int sev_gmem_post_populate(struct kvm *kvm, gfn_t gfn_start, kvm_pfn_t pf
 		if (src) {
 			void *vaddr = kmap_local_pfn(pfn + i);
 
-			ret = copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE);
-			if (ret)
+			if (copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE)) {
+				ret = -EFAULT;
 				goto err;
+			}
 			kunmap_local(vaddr);
 		}