linux-kernel - [PATCH v2] efi/unaccepted: Fix off-by-one when checking for overlapping ranges

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Date:   Fri, 3 Nov 2023 10:13:54 -0500
From:   Michael Roth <michael.roth@....com>
To:     <linux-efi@...r.kernel.org>
CC:     <x86@...nel.org>, <linux-coco@...ts.linux.dev>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Nikolay Borisov <nik.borisov@...e.com>, <stable@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH v2] efi/unaccepted: Fix off-by-one when checking for overlapping ranges

When a task needs to accept memory it will scan the accepting_list
to see if any ranges already being processed by other tasks overlap
with its range. Due to an off-by-one in the range comparisons, a task
might falsely determine that an overlapping range is being accepted,
leading to an unnecessary delay before it begins processing the range.

Fix the off-by-one in the range comparison to prevent this and slightly
improve performance.

Fixes: 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused by parallel memory acceptance")
Link: https://lore.kernel.org/linux-mm/20231101004523.vseyi5bezgfaht5i@amd.com/T/#me2eceb9906fcae5fe958b3fe88e41f920f8335b6
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Signed-off-by: Michael Roth <michael.roth@....com>
---
v2:
 * Improve commit message terminology (Kirill)
---
 drivers/firmware/efi/unaccepted_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index 135278ddaf62..79fb687bb90f 100644
--- a/drivers/firmware/efi/unaccepted_memory.c
+++ b/drivers/firmware/efi/unaccepted_memory.c
@@ -100,7 +100,7 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
 	 * overlap on physical address level.
 	 */
 	list_for_each_entry(entry, &accepting_list, list) {
-		if (entry->end < range.start)
+		if (entry->end <= range.start)
 			continue;
 		if (entry->start >= range.end)
 			continue;
-- 
2.25.1