linux-kernel - [PATCH 3.16 12/25] x86/speculation/taa: Fix printing of TAA_MSG_SMT on IBRS

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Message-ID: <lsq.1573602477.999910664@decadent.org.uk>
Date:   Tue, 12 Nov 2019 23:48:09 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Tyler Hicks" <tyhicks@...onical.com>,
        "Borislav Petkov" <bp@...e.de>
Subject: [PATCH 3.16 12/25] x86/speculation/taa: Fix printing of
 TAA_MSG_SMT on  IBRS_ALL CPUs

3.16.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Josh Poimboeuf <jpoimboe@...hat.com>

commit 012206a822a8b6ac09125bfaa210a95b9eb8f1c1 upstream.

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.

This is not a problem for MDS, because 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 <jpoimboe@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Tyler Hicks <tyhicks@...onical.com>
Reviewed-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/bugs.c | 4 ----
 1 file changed, 4 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -919,10 +919,6 @@ static void update_mds_branch_idle(void)

 void arch_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) {