[SRU][J][PATCH 4/7] arm64: kdump: Do not allocate crash low memory if not needed

Ioanna Alifieraki ioanna-maria.alifieraki at canonical.com
Mon Jul 10 12:56:09 UTC 2023


From: Zhen Lei <thunder.leizhen at huawei.com>

BugLink: https://bugs.launchpad.net/bugs/2024479

When "crashkernel=X,high" is specified, the specified "crashkernel=Y,low"
memory is not required in the following corner cases:
1. If both CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, it means
   that the devices can access any memory.
2. If the system memory is small, the crash high memory may be allocated
   from the DMA zones. If that happens, there's no need to allocate
   another crash low memory because there's already one.

Add condition '(crash_base >= CRASH_ADDR_LOW_MAX)' to determine whether
the 'high' memory is allocated above DMA zones. Note: when both
CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, the entire physical
memory is DMA accessible, CRASH_ADDR_LOW_MAX equals 'PHYS_MASK + 1'.

Signed-off-by: Zhen Lei <thunder.leizhen at huawei.com>
Acked-by: Baoquan He <bhe at redhat.com>
Link: https://lore.kernel.org/r/20220511032033.426-1-thunder.leizhen@huawei.com
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
(backported from commit 8f0f104e2ab6eed4cad3b111dc206f843bda43ea)
[context adjustments in reserve_crashkernel()]
Signed-off-by: Ioanna Alifieraki <ioanna-maria.alifieraki at canonical.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 5 +++--
 arch/arm64/mm/init.c                            | 3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e18af8811ef9..9e8efdf13e21 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -812,7 +812,7 @@
 			low memory is needed to make sure DMA buffers for 32-bit
 			devices won't run out. Kernel would try to allocate
 			at least 256M below 4G automatically.
-			This one let user to specify own low range under 4G
+			This one lets the user specify own low range under 4G
 			for second kernel instead.
 			0: to disable low allocation.
 			It will be ignored when crashkernel=X,high is not used
@@ -821,7 +821,8 @@
 			[KNL, ARM64] range in low memory.
 			This one lets the user specify a low range in the
 			DMA zone for the crash dump kernel.
-			It will be ignored when crashkernel=X,high is not used.
+			It will be ignored when crashkernel=X,high is not used
+			or memory reserved is located in the DMA zones.
 
 	cryptomgr.notests
 			[KNL] Disable crypto self-tests
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9fd61dfd9289..359f5e4f58c0 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -170,7 +170,8 @@ static void __init reserve_crashkernel(void)
 		return;
 	}
 
-	if (crash_low_size && reserve_crashkernel_low(crash_low_size)) {
+	if ((crash_base >= CRASH_ADDR_LOW_MAX) &&
+	     crash_low_size && reserve_crashkernel_low(crash_low_size)) {
 		memblock_free(crash_base, crash_size);
 		return;
 	}
-- 
2.34.1




More information about the kernel-team mailing list