linux-kernel - [PATCH AUTOSEL 6.12 069/486] x86/mm: Check return value from memblock_phys_alloc

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Message-Id: <20250505223922.2682012-69-sashal@kernel.org>
Date: Mon,  5 May 2025 18:32:25 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Philip Redkin <me@...ity.fan>,
	Ingo Molnar <mingo@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...riel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Sasha Levin <sashal@...nel.org>,
	luto@...nel.org,
	peterz@...radead.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	x86@...nel.org
Subject: [PATCH AUTOSEL 6.12 069/486] x86/mm: Check return value from memblock_phys_alloc_range()

From: Philip Redkin <me@...ity.fan>

[ Upstream commit 631ca8909fd5c62b9fda9edda93924311a78a9c4 ]

At least with CONFIG_PHYSICAL_START=0x100000, if there is < 4 MiB of
contiguous free memory available at this point, the kernel will crash
and burn because memblock_phys_alloc_range() returns 0 on failure,
which leads memblock_phys_free() to throw the first 4 MiB of physical
memory to the wolves.

At a minimum it should fail gracefully with a meaningful diagnostic,
but in fact everything seems to work fine without the weird reserve
allocation.

Signed-off-by: Philip Redkin <me@...ity.fan>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Rik van Riel <riel@...riel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: https://lore.kernel.org/r/94b3e98f-96a7-3560-1f76-349eb95ccf7f@rarity.fan
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/mm/init.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 101725c149c42..9cbc1e6057d3c 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -645,8 +645,13 @@ static void __init memory_map_top_down(unsigned long map_start,
 	 */
 	addr = memblock_phys_alloc_range(PMD_SIZE, PMD_SIZE, map_start,
 					 map_end);
-	memblock_phys_free(addr, PMD_SIZE);
-	real_end = addr + PMD_SIZE;
+	if (!addr) {
+		pr_warn("Failed to release memory for alloc_low_pages()");
+		real_end = max(map_start, ALIGN_DOWN(map_end, PMD_SIZE));
+	} else {
+		memblock_phys_free(addr, PMD_SIZE);
+		real_end = addr + PMD_SIZE;
+	}
 
 	/* step_size need to be small so pgt_buf from BRK could cover it */
 	step_size = PMD_SIZE;
-- 
2.39.5