FAILED: patch "[PATCH] KVM: SEV: Ignore Port I/O requests of length '0'" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 3988bd2723de407ae90fa7a6f6029b4e60238c58
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026060433-nectar-retype-0008@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3988bd2723de407ae90fa7a6f6029b4e60238c58 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Fri, 1 May 2026 13:22:29 -0700
Subject: [PATCH] KVM: SEV: Ignore Port I/O requests of length '0'

Explicitly ignore Port I/O requests of length '0' (or count '0'), so that setting up the software scratch area (and other code) doesn't have to worry about underflowing the length, and to allow for WARNing on trying to configure the scratch area with len==0.

Message-ID: <[email protected]>

index e6579ca9f364..52703c954856 100644
@@ -4585,6 +4585,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 			    control->exit_info_1, control->exit_info_2);
 		ret = -EINVAL;
 		break;
+	case SVM_EXIT_IOIO:
+		if (!((control->exit_info_1 & SVM_IOIO_SIZE_MASK) >> SVM_IOIO_SIZE_SHIFT))
+			return 1;
+
+		fallthrough;
 	default:
 		ret = svm_invoke_exit_handler(vcpu, control->exit_code);
 	}

@@ -4605,6 +4610,9 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
 	if (unlikely(check_mul_overflow(count, size, &bytes)))
 		return -EINVAL;
 
+	if (!bytes)
+		return 1;
+
 	r = setup_vmgexit_scratch(svm, in, bytes);
 	if (r)
 		return r;