linux-kernel - [PATCH v5 2/6] mtrr, x86: Fix MTRR lookup to handle inclusive entry

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Message-Id: <1431714237-880-3-git-send-email-toshi.kani@hp.com>
Date:	Fri, 15 May 2015 12:23:53 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	bp@...en8.de, akpm@...ux-foundation.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...hat.com
Cc:	linux-mm@...ck.org, x86@...nel.org, linux-kernel@...r.kernel.org,
	dave.hansen@...el.com, Elliott@...com, pebolle@...cali.nl,
	mcgrof@...e.com, Toshi Kani <toshi.kani@...com>
Subject: [PATCH v5 2/6] mtrr, x86: Fix MTRR lookup to handle inclusive entry

When an MTRR entry is inclusive to a requested range, i.e.
the start and end of the request are not within the MTRR
entry range but the range contains the MTRR entry entirely,
__mtrr_type_lookup() ignores such a case because both
start_state and end_state are set to zero.

This bug can cause the following issues:
1) reserve_memtype() tracks an effective memory type in case
   a request type is WB (ex. /dev/mem blindly uses WB). Missing
   to track with its effective type causes a subsequent request
   to map the same range with the effective type to fail.
2) pud_set_huge() and pmd_set_huge() check if a requested range
   has any overlap with MTRRs. Missing to detect an overlap may
   cause a performance penalty or undefined behavior.

This patch fixes the bug by adding a new flag, 'inclusive',
to detect the inclusive case.  This case is then handled in
the same way as end_state:1 since the first region is the same.
With this fix, __mtrr_type_lookup() handles the inclusive case
properly.

Signed-off-by: Toshi Kani <toshi.kani@...com>
---
 arch/x86/kernel/cpu/mtrr/generic.c |   28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 5b23967..e202d26 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -154,7 +154,7 @@ static u8 __mtrr_type_lookup(u64 start, u64 end, u64 *partial_end, int *repeat)
 
 	prev_match = 0xFF;
 	for (i = 0; i < num_var_ranges; ++i) {
-		unsigned short start_state, end_state;
+		unsigned short start_state, end_state, inclusive;
 
 		if (!(mtrr_state.var_ranges[i].mask_lo & (1 << 11)))
 			continue;
@@ -166,19 +166,27 @@ static u8 __mtrr_type_lookup(u64 start, u64 end, u64 *partial_end, int *repeat)
 
 		start_state = ((start & mask) == (base & mask));
 		end_state = ((end & mask) == (base & mask));
+		inclusive = ((start < base) && (end > base));
 
-		if (start_state != end_state) {
+		if ((start_state != end_state) || inclusive) {
 			/*
 			 * We have start:end spanning across an MTRR.
-			 * We split the region into
-			 * either
-			 * (start:mtrr_end) (mtrr_end:end)
-			 * or
-			 * (start:mtrr_start) (mtrr_start:end)
+			 * We split the region into either
+			 *
+			 * - start_state:1
+			 * (start:mtrr_end)(mtrr_end:end)
+			 * - end_state:1
+			 * (start:mtrr_start)(mtrr_start:end)
+			 * - inclusive:1
+			 * (start:mtrr_start)(mtrr_start:mtrr_end)(mtrr_end:end)
+			 *
 			 * depending on kind of overlap.
-			 * Return the type for first region and a pointer to
-			 * the start of second region so that caller will
-			 * lookup again on the second region.
+			 *
+			 * Return the type of the first region and a pointer
+			 * to the start of next region so that caller will be
+			 * advised to lookup again after having adjusted start
+			 * and end.
+			 *
 			 * Note: This way we handle multiple overlaps as well.
 			 */
 			if (start_state)
--
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