linux-kernel - [PATCH 4/6] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE

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Message-Id: <20230207072902.5528-5-jgross@suse.com>
Date:   Tue,  7 Feb 2023 08:29:00 +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 4/6] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE_INVALID

mtrr_type_lookup() should always return a valid memory type. In case
there is no information available, it should return the default UC.
At the same time the mtrr_type_lookup() stub for the !CONFIG_MTRR
case should set uniform to 1, as if the memory range would be
covered by no MTRR at all.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/include/asm/mtrr.h        | 7 +++++--
 arch/x86/kernel/cpu/mtrr/generic.c | 4 ++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
index 29ec2d6f0537..c12c73d48f08 100644
--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -57,9 +57,12 @@ static inline bool mtrr_enabled(void)
 static inline u8 mtrr_type_lookup(u64 addr, u64 end, u8 *uniform)
 {
 	/*
-	 * Return no-MTRRs:
+	 * Return the default MTRR type, without any known other types in
+	 * that range.
 	 */
-	return MTRR_TYPE_INVALID;
+	*uniform = 1;
+
+	return MTRR_TYPE_UNCACHABLE;
 }
 #define mtrr_save_fixed_ranges(arg) do {} while (0)
 #define mtrr_save_state() do {} while (0)
diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index ee09d359e08f..c749ec4436a1 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -262,10 +262,10 @@ u8 mtrr_type_lookup(u64 start, u64 end, u8 *uniform)
 	end--;
 
 	if (!mtrr_state_set)
-		return MTRR_TYPE_INVALID;
+		return MTRR_TYPE_UNCACHABLE;
 
 	if (!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED))
-		return MTRR_TYPE_INVALID;
+		return MTRR_TYPE_UNCACHABLE;
 
 	/*
 	 * Look up the fixed ranges first, which take priority over
-- 
2.35.3