x86: kexec_file: lift CRASH_MAX_RANGES limit on crash_mem buffer

While CRASH_MAX_RANGES (== 16) seems to be good enough, fixed-number
array is not a good idea in general.

In this patch, size of crash_mem buffer is calculated as before and the
buffer is now dynamically allocated.  This change also allows removing
crash_elf_data structure.

Link: http://lkml.kernel.org/r/20180306102303.9063-6-takahiro.akashi@linaro.org
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Acked-by: Dave Young <dyoung@redhat.com>
Tested-by: Dave Young <dyoung@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/crash.c

@@ -41,32 +41,14 @@
 /* Alignment required for elf header segment */
 #define ELF_CORE_HEADER_ALIGN   4096
 
-/* This primarily represents number of split ranges due to exclusion */
-#define CRASH_MAX_RANGES	16
-
 struct crash_mem_range {
 	u64 start, end;
 };
 
 struct crash_mem {
-	unsigned int nr_ranges;
-	struct crash_mem_range ranges[CRASH_MAX_RANGES];
-};
-
-/* Misc data about ram ranges needed to prepare elf headers */
-struct crash_elf_data {
-	struct kimage *image;
-	/*
-	 * Total number of ram ranges we have after various adjustments for
-	 * crash reserved region, etc.
-	 */
 	unsigned int max_nr_ranges;
-
-	/* Pointer to elf header */
-	void *ehdr;
-	/* Pointer to next phdr */
-	void *bufp;
-	struct crash_mem mem;
+	unsigned int nr_ranges;
+	struct crash_mem_range ranges[0];
 };
 
 /* Used while preparing memory map entries for second kernel */
@@ -218,26 +200,31 @@ static int get_nr_ram_ranges_callback(struct resource *res, void *arg)
 	return 0;
 }
 
-
 /* Gather all the required information to prepare elf headers for ram regions */
-static void fill_up_crash_elf_data(struct crash_elf_data *ced,
-				   struct kimage *image)
+static struct crash_mem *fill_up_crash_elf_data(void)
 {
 	unsigned int nr_ranges = 0;
-
-	ced->image = image;
+	struct crash_mem *cmem;
 
 	walk_system_ram_res(0, -1, &nr_ranges,
 				get_nr_ram_ranges_callback);
+	if (!nr_ranges)
+		return NULL;
 
-	ced->max_nr_ranges = nr_ranges;
+	/*
+	 * Exclusion of crash region and/or crashk_low_res may cause
+	 * another range split. So add extra two slots here.
+	 */
+	nr_ranges += 2;
+	cmem = vzalloc(sizeof(struct crash_mem) +
+			sizeof(struct crash_mem_range) * nr_ranges);
+	if (!cmem)
+		return NULL;
 
-	/* Exclusion of crash region could split memory ranges */
-	ced->max_nr_ranges++;
+	cmem->max_nr_ranges = nr_ranges;
+	cmem->nr_ranges = 0;
 
-	/* If crashk_low_res is not 0, another range split possible */
-	if (crashk_low_res.end)
-		ced->max_nr_ranges++;
+	return cmem;
 }
 
 static int exclude_mem_range(struct crash_mem *mem,
@@ -294,10 +281,8 @@ static int exclude_mem_range(struct crash_mem *mem,
 		return 0;
 
 	/* Split happened */
-	if (i == CRASH_MAX_RANGES - 1) {
-		pr_err("Too many crash ranges after split\n");
+	if (i == mem->max_nr_ranges - 1)
 		return -ENOMEM;
-	}
 
 	/* Location where new range should go */
 	j = i + 1;
@@ -315,11 +300,10 @@ static int exclude_mem_range(struct crash_mem *mem,
 
 /*
  * Look for any unwanted ranges between mstart, mend and remove them. This
- * might lead to split and split ranges are put in ced->mem.ranges[] array
+ * might lead to split and split ranges are put in cmem->ranges[] array
  */
-static int elf_header_exclude_ranges(struct crash_elf_data *ced)
+static int elf_header_exclude_ranges(struct crash_mem *cmem)
 {
-	struct crash_mem *cmem = &ced->mem;
 	int ret = 0;
 
 	/* Exclude crashkernel region */
@@ -338,8 +322,7 @@ static int elf_header_exclude_ranges(struct crash_elf_data *ced)
 
 static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 {
-	struct crash_elf_data *ced = arg;
-	struct crash_mem *cmem = &ced->mem;
+	struct crash_mem *cmem = arg;
 
 	cmem->ranges[cmem->nr_ranges].start = res->start;
 	cmem->ranges[cmem->nr_ranges].end = res->end;
@@ -348,7 +331,7 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg)
 	return 0;
 }
 
-static int prepare_elf64_headers(struct crash_elf_data *ced, bool kernel_map,
+static int prepare_elf64_headers(struct crash_mem *cmem, bool kernel_map,
 		void **addr, unsigned long *sz)
 {
 	Elf64_Ehdr *ehdr;
@@ -357,12 +340,11 @@ static int prepare_elf64_headers(struct crash_elf_data *ced, bool kernel_map,
 	unsigned char *buf, *bufp;
 	unsigned int cpu, i;
 	unsigned long long notes_addr;
-	struct crash_mem *cmem = &ced->mem;
 	unsigned long mstart, mend;
 
 	/* extra phdr for vmcoreinfo elf note */
 	nr_phdr = nr_cpus + 1;
-	nr_phdr += ced->max_nr_ranges;
+	nr_phdr += cmem->nr_ranges;
 
 	/*
 	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
@@ -456,29 +438,27 @@ static int prepare_elf64_headers(struct crash_elf_data *ced, bool kernel_map,
 static int prepare_elf_headers(struct kimage *image, void **addr,
 					unsigned long *sz)
 {
-	struct crash_elf_data *ced;
+	struct crash_mem *cmem;
 	Elf64_Ehdr *ehdr;
 	Elf64_Phdr *phdr;
 	int ret, i;
 
-	ced = kzalloc(sizeof(*ced), GFP_KERNEL);
-	if (!ced)
+	cmem = fill_up_crash_elf_data();
+	if (!cmem)
 		return -ENOMEM;
 
-	fill_up_crash_elf_data(ced, image);
-
-	ret = walk_system_ram_res(0, -1, ced,
+	ret = walk_system_ram_res(0, -1, cmem,
 				prepare_elf64_ram_headers_callback);
 	if (ret)
 		goto out;
 
 	/* Exclude unwanted mem ranges */
-	ret = elf_header_exclude_ranges(ced);
+	ret = elf_header_exclude_ranges(cmem);
 	if (ret)
 		goto out;
 
 	/* By default prepare 64bit headers */
-	ret =  prepare_elf64_headers(ced, IS_ENABLED(CONFIG_X86_64), addr, sz);
+	ret =  prepare_elf64_headers(cmem, IS_ENABLED(CONFIG_X86_64), addr, sz);
 	if (ret)
 		goto out;
 
@@ -496,7 +476,7 @@ static int prepare_elf_headers(struct kimage *image, void **addr,
 			break;
 		}
 out:
-	kfree(ced);
+	vfree(cmem);
 	return ret;
 }