[MODERATED] [PATCH] taa fix

Josh Poimboeuf <[email protected]> Wed, 6 Nov 2019 20:26:46 -0600

Newsgroups	org.kernel.lore.historical-speck
Message-ID	<20191107022646.6h724wh4im5zxvw2@treble>

From: Josh Poimboeuf <[email protected]>
Subject: [PATCH] x86/speculation/taa: Fix TAA_MSG_SMT printk

For new IBRS_ALL CPUs, the Enhanced IBRS check at the beginning of
cpu_bugs_smt_update() causes the function to return early,
unintentionally skipping the MDS and TAA logic.

I don't think it's a problem for MDS, because AFAICT there appears to be
no overlap between IBRS_ALL and MDS-affected CPUs.  So the MDS
mitigation would be disabled and nothing would need to be done in this
function anyway.

But for TAA, the TAA_MSG_SMT string will never get printed on Cascade
Lake and newer.

The check is superfluous anyway: when 'spectre_v2_enabled' is
SPECTRE_V2_IBRS_ENHANCED, 'spectre_v2_user' is always
SPECTRE_V2_USER_NONE, and so the 'spectre_v2_user' switch statement
handles it appropriately by doing nothing.  So just remove the check.

Fixes: 1b42f017415b ("x86/speculation/taa: Add mitigation for TSX Async Abort")
Signed-off-by: Josh Poimboeuf <[email protected]>
---
 arch/x86/kernel/cpu/bugs.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 850005590167..4c7b0fa15a19 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -886,10 +886,6 @@ static void update_mds_branch_idle(void)

 void cpu_bugs_smt_update(void)
 {
-	/* Enhanced IBRS implies STIBP. No update required. */
-	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
-		return;
-
 	mutex_lock(&spec_ctrl_mutex);

 	switch (spectre_v2_user) {
-- 
2.20.1

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