FAILED: patch "[PATCH] KVM: s390: pci: Fix memory accounting for pinned/unpinned" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 36f6999ecde3976731a8bfc0b8e667da6f593069
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026080507-senior-manpower-f5ab@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 36f6999ecde3976731a8bfc0b8e667da6f593069 Mon Sep 17 00:00:00 2001
From: Farhan Ali <[email protected]>
Date: Thu, 23 Jul 2026 15:14:05 -0700
Subject: [PATCH] KVM: s390: pci: Fix memory accounting for pinned/unpinned
 pages

The account_mem() and unaccount_mem() functions call get_uid() which
increments the reference count of struct user_struct on every invocation.
But we don't decrement the count by calling free_uid(). It also
accounted/unaccounted the pages against the current->mm. But its possible
the unaccount_mem() can be called from a different process context than the
one that originally pinned the pages.

Let's fix this by storing the pinning process user_struct and mm_struct
when accounting for pinned pages, and subsequently free these resources
when the pages are unpinned.

Fixes: 3c5a1b6f0a18 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
Cc: [email protected]
Reviewed-by: Christian Borntraeger <[email protected]>
Reviewed-by: Matthew Rosato <[email protected]>
Signed-off-by: Farhan Ali <[email protected]>
Tested-by: Matthew Rosato <[email protected]>
[[email protected]: Fixed whitespace]
Signed-off-by: Christian Borntraeger <[email protected]>

diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
index d2a11cdf6941..0741aed442bc 100644
--- a/arch/s390/kvm/pci.c
+++ b/arch/s390/kvm/pci.c
@@ -190,33 +190,54 @@ static int kvm_zpci_clear_airq(struct zpci_dev *zdev)
 	return cc ? -EIO : 0;
 }
 
-static inline void unaccount_mem(unsigned long nr_pages)
+static inline void unaccount_mem(struct kvm_zdev *kzdev, unsigned long nr_pages)
 {
-	struct user_struct *user = get_uid(current_user());
+	struct user_struct *user = kzdev->user_account;
+	struct mm_struct *mm_account = kzdev->mm_account;
 
-	if (user)
+	if (user) {
 		atomic_long_sub(nr_pages, &user->locked_vm);
-	if (current->mm)
-		atomic64_sub(nr_pages, &current->mm->pinned_vm);
+		free_uid(user);
+		kzdev->user_account = NULL;
+	}
+
+	if (mm_account) {
+		atomic64_sub(nr_pages, &mm_account->pinned_vm);
+		mmdrop(mm_account);
+		kzdev->mm_account = NULL;
+	}
 }
 
-static inline int account_mem(unsigned long nr_pages)
+static inline int account_mem(struct kvm_zdev *kzdev, unsigned long nr_pages)
 {
 	struct user_struct *user = get_uid(current_user());
 	unsigned long page_limit, cur_pages, new_pages;
+	int rc = 0;
 
 	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
 
 	cur_pages = atomic_long_read(&user->locked_vm);
 	do {
 		new_pages = cur_pages + nr_pages;
-		if (new_pages > page_limit)
-			return -ENOMEM;
+		if (new_pages > page_limit) {
+			rc = -ENOMEM;
+			goto out;
+		}
 	} while (!atomic_long_try_cmpxchg(&user->locked_vm, &cur_pages, new_pages));
 
-	atomic64_add(nr_pages, &current->mm->pinned_vm);
+	if (current->mm) {
+		mmgrab(current->mm);
+		atomic64_add(nr_pages, &current->mm->pinned_vm);
+	}
+
+	kzdev->user_account = user;
+	kzdev->mm_account = current->mm;
 
 	return 0;
+
+out:
+	free_uid(user);
+	return rc;
 }
 
 static int kvm_s390_pci_aif_enable(struct zpci_dev *zdev, struct zpci_fib *fib,
@@ -279,7 +300,7 @@ static int kvm_s390_pci_aif_enable(struct zpci_dev *zdev, struct zpci_fib *fib,
 	}
 
 	/* Account for pinned pages, roll back on failure */
-	if (account_mem(pcount))
+	if (account_mem(zdev->kzdev, pcount))
 		goto unpin2;
 
 	/* AISB must be allocated before we can fill in GAITE */
@@ -400,7 +421,7 @@ static int kvm_s390_pci_aif_disable(struct zpci_dev *zdev, bool force)
 		pcount++;
 	}
 	if (pcount > 0)
-		unaccount_mem(pcount);
+		unaccount_mem(kzdev, pcount);
 out:
 	mutex_unlock(&aift->aift_lock);
 
diff --git a/arch/s390/kvm/pci.h b/arch/s390/kvm/pci.h
index ff0972dd5e71..fdf8c7bf4ed0 100644
--- a/arch/s390/kvm/pci.h
+++ b/arch/s390/kvm/pci.h
@@ -22,6 +22,8 @@ struct kvm_zdev {
 	struct kvm *kvm;
 	struct zpci_fib fib;
 	struct list_head entry;
+	struct user_struct *user_account;
+	struct mm_struct *mm_account;
 };
 
 struct zpci_gaite {