[PATCH v6 14/16] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE_INVALID

[Juergen Gross <jgross@suse.com>]

mtrr_type_lookup() should always return a valid memory type. In case
there is no information available, it should return the default UC.

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.

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@linux-foundation.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Michael Kelley <mikelley@microsoft.com>
---
V2:
- always set uniform
- set uniform to 1 in case of disabled MTRRs (Linus Torvalds)
V3:
- adjust include/uapi/asm/mtrr.h comment
---
 arch/x86/include/asm/mtrr.h        | 7 +++++--
 arch/x86/include/uapi/asm/mtrr.h   | 6 +++---
 arch/x86/kernel/cpu/mtrr/generic.c | 4 ++--
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
index 9837fe34e58b..9776a4d576f8 100644
--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -78,9 +78,12 @@ static inline void mtrr_overwrite_state(struct mtrr_var_range *var,
 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/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 2197e835e98c..bb124f16f88c 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -510,13 +510,13 @@ u8 mtrr_type_lookup(u64 start, u64 end, u8 *uniform)
 
 	if (!mtrr_state_set) {
 		*uniform = 0;	/* Uniformity is unknown. */
-		return MTRR_TYPE_INVALID;
+		return MTRR_TYPE_UNCACHABLE;
 	}
 
 	*uniform = 1;
 
 	if (!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED))
-		return MTRR_TYPE_INVALID;
+		return MTRR_TYPE_UNCACHABLE;
 
 	for (i = 0; i < cache_map_n && start < end; i++) {
 		if (start >= cache_map[i].end)
-- 
2.35.3