Re: [PATCH v3] memblock: make memblock_find_in_range method private

On Tue, Aug 03, 2021 at 10:07:37PM +0300, Mike Rapoport wrote:

On Tue, Aug 03, 2021 at 07:05:26PM +0100, Catalin Marinas wrote:

quoted

On Tue, Aug 03, 2021 at 09:42:18AM +0300, Mike Rapoport wrote:

quoted

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 8490ed2917ff..0bffd2d1854f 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -74,6 +74,7 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
 static void __init reserve_crashkernel(void)
 {
 	unsigned long long crash_base, crash_size;
+	unsigned long long crash_max = arm64_dma_phys_limit;
 	int ret;
 
 	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),

@@ -84,33 +85,18 @@ static void __init reserve_crashkernel(void)
 
 	crash_size = PAGE_ALIGN(crash_size);
 
-	if (crash_base == 0) {
-		/* Current arm64 boot protocol requires 2MB alignment */
-		crash_base = memblock_find_in_range(0, arm64_dma_phys_limit,
-				crash_size, SZ_2M);
-		if (crash_base == 0) {
-			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
-				crash_size);
-			return;
-		}
-	} else {
-		/* User specifies base address explicitly. */
-		if (!memblock_is_region_memory(crash_base, crash_size)) {
-			pr_warn("cannot reserve crashkernel: region is not memory\n");
-			return;
-		}
+	/* User specifies base address explicitly. */
+	if (crash_base)
+		crash_max = crash_base + crash_size;
 
-		if (memblock_is_region_reserved(crash_base, crash_size)) {
-			pr_warn("cannot reserve crashkernel: region overlaps reserved memory\n");
-			return;
-		}
-
-		if (!IS_ALIGNED(crash_base, SZ_2M)) {
-			pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n");
-			return;
-		}
+	/* Current arm64 boot protocol requires 2MB alignment */
+	crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
+					       crash_base, crash_max);
+	if (!crash_base) {
+		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
+			crash_size);
+		return;
 	}
-	memblock_reserve(crash_base, crash_size);

We'll miss a bit on debug information provided to the user in case of a
wrong crash_base/size option on the command line. Not sure we care much,
though the alignment would probably be useful (maybe we document it
somewhere).

It is already documented:

Documentation/admin-guide/kdump/kdump.rst:
   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).

Thanks for the pointer.

quoted

What I haven't checked is whether memblock_phys_alloc_range() aims to
get a 2MB aligned end (size) as well. If crash_size is not 2MB aligned,
crash_max wouldn't be either and the above could fail. We only care
about the crash_base to be aligned but the memblock_phys_alloc_range()
doc says that both the start and size would be aligned to this.

The doc lies :)

memblock_phys_alloc_range() boils down to 

	for_each_free_mem_range_reverse(i, nid, flags, &this_start, &this_end,
					NULL) {

		/* clamp this_{start,end} to the user defined limits */

		cand = round_down(this_end - size, align);
		if (cand >= this_start)
			return cand;
	}

Alright, it should work then. For arm64:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

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