Merge tag 'alpha-for-v7.0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/lindholm/alpha

Pull alpha update from Magnus Lindholm:

 - alpha: fix user-space corruption during memory compaction

* tag 'alpha-for-v7.0-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/lindholm/alpha:
  alpha: fix user-space corruption during memory compaction

Author: torvalds

arch/alpha/include/asm/pgtable.h

@@ -17,6 +17,7 @@
 #include <asm/processor.h>	/* For TASK_SIZE */
 #include <asm/machvec.h>
 #include <asm/setup.h>
+#include <linux/page_table_check.h>
 
 struct mm_struct;
 struct vm_area_struct;
@@ -183,6 +184,9 @@ extern inline void pud_set(pud_t * pudp, pmd_t * pmdp)
 { pud_val(*pudp) = _PAGE_TABLE | ((((unsigned long) pmdp) - PAGE_OFFSET) << (32-PAGE_SHIFT)); }
 
 
+extern void migrate_flush_tlb_page(struct vm_area_struct *vma,
+					unsigned long addr);
+
 extern inline unsigned long
 pmd_page_vaddr(pmd_t pmd)
 {
@@ -202,7 +206,7 @@ extern inline int pte_none(pte_t pte)		{ return !pte_val(pte); }
 extern inline int pte_present(pte_t pte)	{ return pte_val(pte) & _PAGE_VALID; }
 extern inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
 {
-	pte_val(*ptep) = 0;
+	WRITE_ONCE(pte_val(*ptep), 0);
 }
 
 extern inline int pmd_none(pmd_t pmd)		{ return !pmd_val(pmd); }
@@ -264,6 +268,33 @@ extern inline pte_t * pte_offset_kernel(pmd_t * dir, unsigned long address)
 
 extern pgd_t swapper_pg_dir[1024];
 
+#ifdef CONFIG_COMPACTION
+#define __HAVE_ARCH_PTEP_GET_AND_CLEAR
+
+static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
+					unsigned long address,
+					pte_t *ptep)
+{
+	pte_t pte = READ_ONCE(*ptep);
+
+	pte_clear(mm, address, ptep);
+	return pte;
+}
+
+#define __HAVE_ARCH_PTEP_CLEAR_FLUSH
+
+static inline pte_t ptep_clear_flush(struct vm_area_struct *vma,
+				unsigned long addr, pte_t *ptep)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	pte_t pte = ptep_get_and_clear(mm, addr, ptep);
+
+	page_table_check_pte_clear(mm, pte);
+	migrate_flush_tlb_page(vma, addr);
+	return pte;
+}
+
+#endif
 /*
  * The Alpha doesn't have any external MMU info:  the kernel page
  * tables contain all the necessary information.

arch/alpha/include/asm/tlbflush.h

@@ -58,7 +58,9 @@ flush_tlb_other(struct mm_struct *mm)
 	unsigned long *mmc = &mm->context[smp_processor_id()];
 	/* Check it's not zero first to avoid cacheline ping pong
 	   when possible.  */
-	if (*mmc) *mmc = 0;
+
+	if (READ_ONCE(*mmc))
+		WRITE_ONCE(*mmc, 0);
 }
 
 #ifndef CONFIG_SMP

arch/alpha/mm/Makefile

@@ -3,4 +3,4 @@
 # Makefile for the linux alpha-specific parts of the memory manager.
 #
 
-obj-y	:= init.o fault.o
+obj-y	:= init.o fault.o tlbflush.o

arch/alpha/mm/tlbflush.c

@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Alpha TLB shootdown helpers
+ *
+ * Copyright (C) 2025 Magnus Lindholm <linmag7@gmail.com>
+ *
+ * Alpha-specific TLB flush helpers that cannot be expressed purely
+ * as inline functions.
+ *
+ * These helpers provide combined MM context handling (ASN rollover)
+ * and immediate TLB invalidation for page migration and memory
+ * compaction paths, where lazy shootdowns are insufficient.
+ */
+
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/sched.h>
+#include <asm/tlbflush.h>
+#include <asm/pal.h>
+#include <asm/mmu_context.h>
+
+#define asn_locked() (cpu_data[smp_processor_id()].asn_lock)
+
+/*
+ * Migration/compaction helper: combine mm context (ASN) handling with an
+ * immediate per-page TLB invalidate and (for exec) an instruction barrier.
+ *
+ * This mirrors the SMP combined IPI handler semantics, but runs locally on UP.
+ */
+#ifndef CONFIG_SMP
+void migrate_flush_tlb_page(struct vm_area_struct *vma,
+					   unsigned long addr)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	int tbi_type = (vma->vm_flags & VM_EXEC) ? 3 : 2;
+
+	/*
+	 * First do the mm-context side:
+	 * If we're currently running this mm, reload a fresh context ASN.
+	 * Otherwise, mark context invalid.
+	 *
+	 * On UP, this is mostly about matching the SMP semantics and ensuring
+	 * exec/i-cache tagging assumptions hold when compaction migrates pages.
+	 */
+	if (mm == current->active_mm)
+		flush_tlb_current(mm);
+	else
+		flush_tlb_other(mm);
+
+	/*
+	 * Then do the immediate translation kill for this VA.
+	 * For exec mappings, order instruction fetch after invalidation.
+	 */
+	tbi(tbi_type, addr);
+}
+
+#else
+struct tlb_mm_and_addr {
+	struct mm_struct *mm;
+	unsigned long addr;
+	int tbi_type;	/* 2 = DTB, 3 = ITB+DTB */
+};
+
+static void ipi_flush_mm_and_page(void *x)
+{
+	struct tlb_mm_and_addr *d = x;
+
+	/* Part 1: mm context side (Alpha uses ASN/context as a key mechanism). */
+	if (d->mm == current->active_mm && !asn_locked())
+		__load_new_mm_context(d->mm);
+	else
+		flush_tlb_other(d->mm);
+
+	/* Part 2: immediate per-VA invalidation on this CPU. */
+	tbi(d->tbi_type, d->addr);
+}
+
+void migrate_flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct tlb_mm_and_addr d = {
+		.mm = mm,
+		.addr = addr,
+		.tbi_type = (vma->vm_flags & VM_EXEC) ? 3 : 2,
+	};
+
+	/*
+	 * One synchronous rendezvous: every CPU runs ipi_flush_mm_and_page().
+	 * This is the "combined" version of flush_tlb_mm + per-page invalidate.
+	 */
+	preempt_disable();
+	on_each_cpu(ipi_flush_mm_and_page, &d, 1);
+
+	/*
+	 * mimic flush_tlb_mm()'s mm_users<=1 optimization.
+	 */
+	if (atomic_read(&mm->mm_users) <= 1) {
+
+		int cpu, this_cpu;
+		this_cpu = smp_processor_id();
+
+		for (cpu = 0; cpu < NR_CPUS; cpu++) {
+			if (!cpu_online(cpu) || cpu == this_cpu)
+				continue;
+			if (READ_ONCE(mm->context[cpu]))
+				WRITE_ONCE(mm->context[cpu], 0);
+		}
+	}
+	preempt_enable();
+}
+
+#endif