[PATCH 4.9 15/31] x86/speculation/taa: Fix printing of TAA_MSG_SMT on IBRS_ALL CPUs

Greg Kroah-Hartman
2019-11-15T06:22:13Z

From: Josh Poimboeuf <jpoimboe@redhat.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@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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
@@ -882,10 +882,6 @@ 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) {