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[SRU,Jammy,6/7] intel_idle: Fix SPR C6 optimization

Message ID 20230207175857.164618-7-joseph.salisbury@canonical.com
State New
Headers show
Series [SRU,Jammy,1/7] intel_idle: add SPR support | expand

Commit Message

Joseph Salisbury Feb. 7, 2023, 5:58 p.m. UTC 
From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

BugLink: https://bugs.launchpad.net/bugs/2003267

The Sapphire Rapids (SPR) C6 optimization was added to the end of the
'spr_idle_state_table_update()' function. However, the function has a
'return' which may happen before the optimization has a chance to run.
And this may prevent the optimization from happening.

This is an unlikely scenario, but possible if user boots with, say,
the 'intel_idle.preferred_cstates=6' kernel boot option.

This patch fixes the issue by eliminating the problematic 'return'
statement.

Fixes: 3a9cf77b60dc ("intel_idle: add core C6 optimization for SPR")
Suggested-by: Jan Beulich <jbeulich@suse.com>
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
[ rjw: Minor changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit 7eac3bd38d18cd3317756649921b8264ddfee692)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
---
 drivers/idle/intel_idle.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)
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Patch

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 7ff47d9f6822..97b3891c500e 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -1601,11 +1601,9 @@  static void __init spr_idle_state_table_update(void)
 	unsigned long long msr;
 
 	/* Check if user prefers C1E over C1. */
-	if (preferred_states_mask & BIT(2)) {
-		if (preferred_states_mask & BIT(1))
-			/* Both can't be enabled, stick to the defaults. */
-			return;
-
+	if ((preferred_states_mask & BIT(2)) &&
+	    !(preferred_states_mask & BIT(1))) {
+		/* Disable C1 and enable C1E. */
 		spr_cstates[0].flags |= CPUIDLE_FLAG_UNUSABLE;
 		spr_cstates[1].flags &= ~CPUIDLE_FLAG_UNUSABLE;