[PATCH RFC v2 19/29] mm: asi: Stabilize CR3 in switch_mm_irqs_off()

[Brendan Jackman]

An ASI-restricted CR3 is unstable as interrupts can cause ASI-exits.
Although we already unconditionally ASI-exit during context-switch, and
before returning from the VM-run path, it's still possible to reach
switch_mm_irqs_off() in a restricted context, because KVM code updates
static keys, which requires using a temporary mm.

Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
 arch/x86/mm/tlb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index c55733e144c7538ce7f97b74ea2b1b9c22497c32..ce5598f96ea7a84dc0e8623022ab5bfbba401b48 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -546,6 +546,9 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next,
 	bool need_flush;
 	u16 new_asid;
 
+	/* Stabilize CR3, before reading or writing CR3 */
+	asi_exit();
+
 	/* We don't want flush_tlb_func() to run concurrently with us. */
 	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
 		WARN_ON_ONCE(!irqs_disabled());

-- 
2.47.1.613.gc27f4b7a9f-goog