Attachment 823583 Details for Bug 1139073

[patch] follow up fix

x86-speculation-taa-Fix-TAA_MSG_SMT-printk.patch (text/plain), 1.49 KB, created by Michal Hocko on 2019-11-07 08:51:45 UTC

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Creator: Michal Hocko

Created: 2019-11-07 08:51:45 UTC

Size: 1.49 KB

patch

obsolete

>From: Josh Poimboeuf <jpoimboe@redhat.com>
>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 <jpoimboe@redhat.com>
>---
> 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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Attachments on bug 1139073: 820901 | 823583