[PATCH 1/5] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

From: Zhen Lei <thunder.leizhen@huawei.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	<x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
	Eric Biederman <ebiederm@xmission.com>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	<devicetree@vger.kernel.org>, Dave Young <dyoung@redhat.com>,
	Baoquan He <bhe@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
	<kexec@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	Jonathan Corbet <corbet@lwn.net>, <linux-doc@vger.kernel.org>
Cc: Zhen Lei <thunder.leizhen@huawei.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Feng Zhou <zhoufeng.zf@bytedance.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Chen Zhou <dingguo.cz@antgroup.com>,
	"John Donnelly" <John.p.donnelly@oracle.com>,
	Dave Kleikamp <dave.kleikamp@oracle.com>
Subject: [PATCH 1/5] arm64: kdump: Provide default size when crashkernel=Y,low is not specified
Date: Mon, 13 Jun 2022 16:09:28 +0800	[thread overview]
Message-ID: <20220613080932.663-2-thunder.leizhen@huawei.com> (raw)
In-Reply-To: <20220613080932.663-1-thunder.leizhen@huawei.com>

To be consistent with the implementation of x86 and improve cross-platform
user experience. Try to allocate at least 256 MiB low memory automatically
when crashkernel=Y,low is not specified.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  8 +-------
 arch/arm64/mm/init.c                            | 12 +++++++++++-
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 8090130b544b070..61b179232b68001 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -843,7 +843,7 @@
 			available.
 			It will be ignored if crashkernel=X is specified.
 	crashkernel=size[KMG],low
-			[KNL, X86-64] range under 4G. When crashkernel=X,high
+			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
 			is passed, kernel could allocate physical memory region
 			above 4G, that cause second kernel crash on system
 			that require some amount of low memory, e.g. swiotlb
@@ -857,12 +857,6 @@
 			It will be ignored when crashkernel=X,high is not used
 			or memory reserved is below 4G.
 
-			[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
-			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 339ee84e5a61a0b..5390f361208ccf7 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
 #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
 #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
 
+/*
+ * This is an empirical value in x86_64 and taken here directly. Please
+ * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
+ * details.
+ */
+#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
+	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
+
 static int __init reserve_crashkernel_low(unsigned long long low_size)
 {
 	unsigned long long low_base;
@@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
 		 * is not allowed.
 		 */
 		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
-		if (ret && (ret != -ENOENT))
+		if (ret == -ENOENT)
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+		else if (ret)
 			return;
 
 		crash_max = CRASH_ADDR_HIGH_MAX;
-- 
2.25.1


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