linux-kernel - [PATCH v3 01/10] x86/mtrr: add comment for set_mtrr

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Date:   Thu,  8 Sep 2022 10:49:05 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v3 01/10] x86/mtrr: add comment for set_mtrr_state() serialization

Add a comment how set_mtrr_state() is needing serialization.

Suggested-by: Borislav Petkov <bp@...en8.de>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
V3:
- new patch instead of old patch 1
---
 arch/x86/kernel/cpu/mtrr/generic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 558108296f3c..cd64eab02393 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -684,7 +684,10 @@ static u32 deftype_lo, deftype_hi;
 /**
  * set_mtrr_state - Set the MTRR state for this CPU.
  *
- * NOTE: The CPU must already be in a safe state for MTRR changes.
+ * NOTE: The CPU must already be in a safe state for MTRR changes, including
+ *       measures that only a single CPU can be active in set_mtrr_state() in
+ *       order to not be subject to races for usage of deftype_lo (this is
+ *       accomplished by taking set_atomicity_lock).
  * RETURNS: 0 if no changes made, else a mask indicating what was changed.
  */
 static unsigned long set_mtrr_state(void)
-- 
2.35.3