[PATCH v2 6/7] x86/power: Sprinkle some noinstr

Peter Zijlstra
2023-01-16T14:52:51Z

Ensure no compiler instrumentation sneaks in while restoring the CPU
state. Specifically we can't handle CALL/RET until GS is restored.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/power/cpu.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -192,7 +192,7 @@ static void fix_processor_context(void)
* The asm code that gets us here will have restored a usable GDT, although
* it will be pointing to the wrong alias.
*/
-static void notrace __restore_processor_state(struct saved_context *ctxt)
+static __always_inline void __restore_processor_state(struct saved_context *ctxt)
{
struct cpuinfo_x86 *c;

@@ -235,6 +235,13 @@ static void notrace __restore_processor_
loadsegment(fs, __KERNEL_PERCPU);
#endif

+ /*
+ * Definitely wrong, but at this point we should have at least enough
+ * to do CALL/RET (consider SKL callthunks) and this avoids having
+ * to deal with the noinstr explosion for now :/
+ */
+ instrumentation_begin();
+
/* Restore the TSS, RO GDT, LDT, and usermode-relevant MSRs. */
fix_processor_context();

@@ -276,10 +283,12 @@ static void notrace __restore_processor_
* because some of the MSRs are "emulated" in microcode.
*/
msr_restore_context(ctxt);
+
+ instrumentation_end();
}

/* Needed by apm.c */
-void notrace restore_processor_state(void)
+void noinstr restore_processor_state(void)
{
__restore_processor_state(&saved_context);
}