Merge tag 'locking-urgent-2026-09-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tipgrafted

Pull futex fix from Ingo Molnar:

 - Also allocate a default private futex hash on vfork() as well, to
   avoid races with (private) futex waiters (Peter Zijlstra)

* tag 'locking-urgent-2026-09-20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Also allocate private hash on vfork()

1 files changed, 61 insertions, 0 deletions

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
new file mode 100644
index 000000000..14cd43d4d
--- /dev/null
+++ b/arch/x86/entry/common.c
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/entry-common.h>
+#include <linux/kvm_types.h>
+#include <linux/hrtimer_rearm.h>
+#include <asm/fred.h>
+#include <asm/desc.h>
+
+#if IS_ENABLED(CONFIG_KVM_INTEL)
+/*
+ * On VMX, NMIs and IRQs (as configured by KVM) are acknowledged by hardware as
+ * part of the VM-Exit, i.e. the event itself is consumed as part the VM-Exit.
+ * x86_entry_from_kvm() is invoked by KVM to effectively forward NMIs and IRQs
+ * to the kernel for servicing.  On SVM, a.k.a. AMD, the NMI/IRQ VM-Exit is
+ * purely a signal that an NMI/IRQ is pending, i.e. the event that triggered
+ * the VM-Exit is held pending until it's unblocked in the host.
+ */
+noinstr void x86_entry_from_kvm(unsigned int event_type, unsigned int vector)
+{
+	if (event_type == EVENT_TYPE_EXTINT) {
+#ifdef CONFIG_X86_64
+		/*
+		 * Use FRED dispatch, even when running IDT. The dispatch
+		 * tables are kept in sync between FRED and IDT, and the FRED
+		 * dispatch works well with CFI.
+		 */
+		fred_entry_from_kvm(event_type, vector);
+#else
+		idt_entry_from_kvm(vector);
+#endif
+		/*
+		 * Strictly speaking, only the NMI path requires noinstr.
+		 */
+		instrumentation_begin();
+		/*
+		 * KVM/VMX will dispatch from IRQ-disabled but for a context
+		 * that will have IRQs-enabled. This confuses the entry code
+		 * and it will not have reprogrammed the timer. Do so now.
+		 */
+		hrtimer_rearm_deferred();
+		instrumentation_end();
+
+		return;
+	}
+
+	WARN_ON_ONCE(event_type != EVENT_TYPE_NMI);
+
+#ifdef CONFIG_X86_64
+	if (cpu_feature_enabled(X86_FEATURE_FRED))
+		return fred_entry_from_kvm(event_type, vector);
+#endif
+
+	/*
+	 * Notably, we must use IDT dispatch for NMI when running in IDT mode.
+	 * The FRED NMI context is significantly different and will not work
+	 * right (specifically FRED fixed the NMI recursion issue).
+	 */
+	idt_do_nmi_irqoff();
+}
+EXPORT_SYMBOL_FOR_KVM(x86_entry_from_kvm);
+#endif