Merge tag 'kvmarm-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD

KVM/arm64 updates for 6.12

* New features:

  - Add a Stage-2 page table dumper, reusing the main ptdump
    infrastructure, and allowing easier debugging of the our
    page-table infrastructure

  - Add FP8 support to the KVM/arm64 floating point handling.

  - Add NV support for the AT family of instructions, which mostly
    results in adding a page table walker that deals with most of the
    complexity of the architecture.

* Improvements, fixes and cleanups:

  - Add selftest checks for a bunch of timer emulation corner cases

  - Fix the multiple of cases where KVM/arm64 doesn't correctly handle
    the guest trying to use a GICv3 that isn't advertised

  - Remove REG_HIDDEN_USER from the sysreg infrastructure, making
    things little more simple

  - Prevent MTE tags being restored by userspace if we are actively
    logging writes, as that's a recipe for disaster

  - Correct the refcount on a page that is not considered for MTE tag
    copying (such as a device)

  - Relax the synchronisation when walking a page table to split block
    mappings, moving it at the end the walk, as there is no need to
    perform it on every store.

  - Fix boundary check when transfering memory using FFA

  - Fix pKVM TLB invalidation, only affecting currently out of tree
    code but worth addressing for peace of mind

1 files changed, 22 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index cc760491f201..18bdc87209d0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,11 +2053,24 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
  */
 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret)
 {
-	bool thread = flags & PIDFD_THREAD;
-
-	if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID))
+	if (!pid)
 		return -EINVAL;
 
+	scoped_guard(rcu) {
+		struct task_struct *tsk;
+
+		if (flags & PIDFD_THREAD)
+			tsk = pid_task(pid, PIDTYPE_PID);
+		else
+			tsk = pid_task(pid, PIDTYPE_TGID);
+		if (!tsk)
+			return -EINVAL;
+
+		/* Don't create pidfds for kernel threads for now. */
+		if (tsk->flags & PF_KTHREAD)
+			return -EINVAL;
+	}
+
 	return __pidfd_prepare(pid, flags, ret);
 }
 
@@ -2403,6 +2416,12 @@ __latent_entropy struct task_struct *copy_process(
 	if (clone_flags & CLONE_PIDFD) {
 		int flags = (clone_flags & CLONE_THREAD) ? PIDFD_THREAD : 0;
 
+		/* Don't create pidfds for kernel threads for now. */
+		if (args->kthread) {
+			retval = -EINVAL;
+			goto bad_fork_free_pid;
+		}
+
 		/* Note that no task has been attached to @pid yet. */
 		retval = __pidfd_prepare(pid, flags, &pidfile);
 		if (retval < 0)