KVM: SVM: Fix a missing kunmap_local() in sev_gmem_post_populate()

sev_gmem_post_populate() needs to unmap the target vaddr after
copy_from_user() to the vaddr fails.

Fixes: dee5a47 ("KVM: SEV: Add KVM_SEV_SNP_LAUNCH_UPDATE command")
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Link: https://patch.msgid.link/20260108214622.1084057-2-michael.roth@amd.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: yanzhao56

arch/x86/kvm/svm/sev.c

@@ -2296,6 +2296,7 @@ static int sev_gmem_post_populate(struct kvm *kvm, gfn_t gfn_start, kvm_pfn_t pf
 			void *vaddr = kmap_local_pfn(pfn + i);
 
 			if (copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE)) {
+				kunmap_local(vaddr);
 				ret = -EFAULT;
 				goto err;
 			}