[PATCH 01/23] x86/srso: Fix srso_show_state() side effect

[Josh Poimboeuf]

Reading the 'spec_rstack_overflow' sysfs file can trigger an unnecessary
MSR write, and possibly even a (handled) exception if the microcode
hasn't been updated.

Avoid all that by just checking X86_FEATURE_IBPB_BRTYPE instead, which
gets set by srso_select_mitigation() if the updated microcode exists.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f081d26616ac..bdd3e296f72b 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2717,7 +2717,7 @@ static ssize_t srso_show_state(char *buf)
 
 	return sysfs_emit(buf, "%s%s\n",
 			  srso_strings[srso_mitigation],
-			  (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));
+			  boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) ? "" : ", no microcode");
 }
 
 static ssize_t gds_show_state(char *buf)
-- 
2.41.0