linux-kernel - [PATCH v2 8/8] x86/mtrr: drop sanity check in mtrr_type_lookup

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Date:   Thu,  9 Feb 2023 08:22:20 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org, 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 v2 8/8] x86/mtrr: drop sanity check in mtrr_type_lookup_fixed()

mtrr_type_lookup_fixed() contains a sanity check for the case it is
being called with a start address above 1 MB. As it is static and it
is called only iff the start address is below 1MB, this sanity check
can be dropped.

This will remove the last case where mtrr_type_lookup() can return
MTRR_TYPE_INVALID, so adjust the comment in include/uapi/asm/mtrr.h.

Note that removing the MTRR_TYPE_INVALID #define from that header
could break user code, so it has to stay.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/include/uapi/asm/mtrr.h   | 6 +++---
 arch/x86/kernel/cpu/mtrr/generic.c | 6 +-----
 2 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/uapi/asm/mtrr.h b/arch/x86/include/uapi/asm/mtrr.h
index 376563f2bac1..4aa05c2ffa78 100644
--- a/arch/x86/include/uapi/asm/mtrr.h
+++ b/arch/x86/include/uapi/asm/mtrr.h
@@ -115,9 +115,9 @@ struct mtrr_state_type {
 #define MTRR_NUM_TYPES       7
 
 /*
- * Invalid MTRR memory type.  mtrr_type_lookup() returns this value when
- * MTRRs are disabled.  Note, this value is allocated from the reserved
- * values (0x7-0xff) of the MTRR memory types.
+ * Invalid MTRR memory type.  No longer used outside of MTRR code.
+ * Note, this value is allocated from the reserved values (0x7-0xff) of
+ * the MTRR memory types.
  */
 #define MTRR_TYPE_INVALID    0xff
 
diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index afb59ff2cc00..575b050a55bf 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -114,16 +114,12 @@ static int check_type_overlap(u8 *prev, u8 *curr)
  *  0xC0000 - 0xFFFFF : This range is divided into sixty-four 4KB sub-ranges
  *
  * Return Values:
- * MTRR_TYPE_(type)  - Matched memory type
- * MTRR_TYPE_INVALID - Unmatched
+ * MTRR_TYPE_(type)  - Memory type
  */
 static u8 mtrr_type_lookup_fixed(u64 start, u64 end)
 {
 	int idx;
 
-	if (start >= 0x100000)
-		return MTRR_TYPE_INVALID;
-
 	/* 0x0 - 0x7FFFF */
 	if (start < 0x80000) {
 		idx = 0;
-- 
2.35.3