[PATCH 3/7] x86/mm: Make use/unuse_temporary_mm() non-static

[Peter Zijlstra <peterz@infradead.org>]

From: Andy Lutomirski <luto@kernel.org>

This prepares them for use outside of the alternative machinery.
The code is unchanged.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d1205bc7e165e249c52b7fe8cb1254f06e8a0e2a.1641659630.git.luto@kernel.org
---
 arch/x86/include/asm/mmu_context.h |    7 +++
 arch/x86/kernel/alternative.c      |   68 -------------------------------------
 arch/x86/mm/tlb.c                  |   63 ++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 68 deletions(-)

--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -263,4 +263,11 @@ unsigned long __get_current_cr3_fast(voi
 
 #include <asm-generic/mmu_context.h>
 
+typedef struct {
+	struct mm_struct *mm;
+} temp_mm_state_t;
+
+extern temp_mm_state_t use_temporary_mm(struct mm_struct *mm);
+extern void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state);
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1774,77 +1774,9 @@ void __init_or_module text_poke_early(vo
 	}
 }
 
-typedef struct {
-	struct mm_struct *mm;
-} temp_mm_state_t;
-
-/*
- * Using a temporary mm allows to set temporary mappings that are not accessible
- * by other CPUs. Such mappings are needed to perform sensitive memory writes
- * that override the kernel memory protections (e.g., W^X), without exposing the
- * temporary page-table mappings that are required for these write operations to
- * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
- * mapping is torn down.
- *
- * Context: The temporary mm needs to be used exclusively by a single core. To
- *          harden security IRQs must be disabled while the temporary mm is
- *          loaded, thereby preventing interrupt handler bugs from overriding
- *          the kernel memory protection.
- */
-static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
-{
-	temp_mm_state_t temp_state;
-
-	lockdep_assert_irqs_disabled();
-
-	/*
-	 * Make sure not to be in TLB lazy mode, as otherwise we'll end up
-	 * with a stale address space WITHOUT being in lazy mode after
-	 * restoring the previous mm.
-	 */
-	if (this_cpu_read(cpu_tlbstate_shared.is_lazy))
-		leave_mm();
-
-	temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
-	switch_mm_irqs_off(NULL, mm, current);
-
-	/*
-	 * If breakpoints are enabled, disable them while the temporary mm is
-	 * used. Userspace might set up watchpoints on addresses that are used
-	 * in the temporary mm, which would lead to wrong signals being sent or
-	 * crashes.
-	 *
-	 * Note that breakpoints are not disabled selectively, which also causes
-	 * kernel breakpoints (e.g., perf's) to be disabled. This might be
-	 * undesirable, but still seems reasonable as the code that runs in the
-	 * temporary mm should be short.
-	 */
-	if (hw_breakpoint_active())
-		hw_breakpoint_disable();
-
-	return temp_state;
-}
-
 __ro_after_init struct mm_struct *poking_mm;
 __ro_after_init unsigned long poking_addr;
 
-static inline void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state)
-{
-	lockdep_assert_irqs_disabled();
-
-	switch_mm_irqs_off(NULL, prev_state.mm, current);
-
-	/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
-	cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(mm));
-
-	/*
-	 * Restore the breakpoints if they were disabled before the temporary mm
-	 * was loaded.
-	 */
-	if (hw_breakpoint_active())
-		hw_breakpoint_restore();
-}
-
 static void text_poke_memcpy(void *dst, const void *src, size_t len)
 {
 	memcpy(dst, src, len);
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -674,6 +674,69 @@ void enter_lazy_tlb(struct mm_struct *mm
 }
 
 /*
+ * Using a temporary mm allows to set temporary mappings that are not accessible
+ * by other CPUs. Such mappings are needed to perform sensitive memory writes
+ * that override the kernel memory protections (e.g., W^X), without exposing the
+ * temporary page-table mappings that are required for these write operations to
+ * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
+ * mapping is torn down.
+ *
+ * Context: The temporary mm needs to be used exclusively by a single core. To
+ *          harden security IRQs must be disabled while the temporary mm is
+ *          loaded, thereby preventing interrupt handler bugs from overriding
+ *          the kernel memory protection.
+ */
+temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
+{
+	temp_mm_state_t temp_state;
+
+	lockdep_assert_irqs_disabled();
+
+	/*
+	 * Make sure not to be in TLB lazy mode, as otherwise we'll end up
+	 * with a stale address space WITHOUT being in lazy mode after
+	 * restoring the previous mm.
+	 */
+	if (this_cpu_read(cpu_tlbstate_shared.is_lazy))
+		leave_mm();
+
+	temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+	switch_mm_irqs_off(NULL, mm, current);
+
+	/*
+	 * If breakpoints are enabled, disable them while the temporary mm is
+	 * used. Userspace might set up watchpoints on addresses that are used
+	 * in the temporary mm, which would lead to wrong signals being sent or
+	 * crashes.
+	 *
+	 * Note that breakpoints are not disabled selectively, which also causes
+	 * kernel breakpoints (e.g., perf's) to be disabled. This might be
+	 * undesirable, but still seems reasonable as the code that runs in the
+	 * temporary mm should be short.
+	 */
+	if (hw_breakpoint_active())
+		hw_breakpoint_disable();
+
+	return temp_state;
+}
+
+void unuse_temporary_mm(struct mm_struct *mm, temp_mm_state_t prev_state)
+{
+	lockdep_assert_irqs_disabled();
+	switch_mm_irqs_off(NULL, prev_state.mm, current);
+
+	/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
+	cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(mm));
+
+	/*
+	 * Restore the breakpoints if they were disabled before the temporary mm
+	 * was loaded.
+	 */
+	if (hw_breakpoint_active())
+		hw_breakpoint_restore();
+}
+
+/*
  * Call this when reinitializing a CPU.  It fixes the following potential
  * problems:
  *