EFI runtime services should use temporary mms, but EFI runtime services
want IRQs on. Preemption must still be disabled in a temporary mm context.
At some point, the entirely temporary mm mechanism should be moved out of
arch code.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/mm/tlb.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 4e371f30e2ab..36ce9dffb963 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -708,18 +708,23 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
* 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.
+ * mapping is torn down. Temporary mms can also be used for EFI runtime service
+ * calls or similar functionality.
*
- * 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.
+ * It is illegal to schedule while using a temporary mm -- the context switch
+ * code is unaware of the temporary mm and does not know how to context switch.
+ * Use a real (non-temporary) mm in a kernel thread if you need to sleep.
+ *
+ * Note: For sensitive memory writes, the temporary mm needs to be used
+ * exclusively by a single core, and IRQs should 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();
+ lockdep_assert_preemption_disabled();
/*
* Make sure not to be in TLB lazy mode, as otherwise we'll end up
@@ -751,7 +756,7 @@ temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
void unuse_temporary_mm(temp_mm_state_t prev_state)
{
- lockdep_assert_irqs_disabled();
+ lockdep_assert_preemption_disabled();
switch_mm_irqs_off(NULL, prev_state.mm, current);
/*
--
2.33.1
