[RFC 1/3] crash_dump: Parse the CMA's mem_map in kdump

[Pingfan Liu <kernelfans@gmail.com>]

From: Pingfan Liu <piliu@redhat.com>

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
To: kexec@lists.infradead.org
---
 include/linux/kexec.h |  1 +
 init/main.c           |  4 +++
 kernel/crash_dump.c   | 80 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 8227455192b7..95e19c814c93 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -410,6 +410,7 @@ extern bool kexec_in_progress;
 
 int crash_shrink_memory(unsigned long new_size);
 ssize_t crash_get_memory_size(void);
+void kdump_kernel_reuse_mem(void);
 
 #ifndef arch_kexec_protect_crashkres
 /*
diff --git a/init/main.c b/init/main.c
index e24b0780fdff..ed90097caaa8 100644
--- a/init/main.c
+++ b/init/main.c
@@ -99,6 +99,7 @@
 #include <linux/init_syscalls.h>
 #include <linux/stackdepot.h>
 #include <linux/randomize_kstack.h>
+#include <linux/kexec.h>
 #include <net/net_namespace.h>
 
 #include <asm/io.h>
@@ -1068,6 +1069,9 @@ void start_kernel(void)
 	arch_post_acpi_subsys_init();
 	kcsan_init();
 
+	/* */
+	kdump_kernel_reuse_mem();
+
 	/* Do the rest non-__init'ed, we're now alive */
 	arch_call_rest_init();
 
diff --git a/kernel/crash_dump.c b/kernel/crash_dump.c
index 92da32275af5..4605005f9534 100644
--- a/kernel/crash_dump.c
+++ b/kernel/crash_dump.c
@@ -4,6 +4,7 @@
 #include <linux/init.h>
 #include <linux/errno.h>
 #include <linux/export.h>
+#include <linux/cc_platform.h>
 
 /*
  * stores the physical address of elf header of crash image
@@ -39,3 +40,82 @@ static int __init setup_elfcorehdr(char *arg)
 	return end > arg ? 0 : -EINVAL;
 }
 early_param("elfcorehdr", setup_elfcorehdr);
+
+u64 kdump_cma_pfn;
+u64 kdump_cma_pg_cnt;
+u64 kdump_cma_pg_paddr;
+
+/* In old kernel, wreck should correspond to pfn */
+static void check_poison_page(struct page *wreck, int cnt, unsigned long pfn)
+{
+	int i = 0;
+	int order;
+	/* Info copied from old kernel */
+	struct page *check = wreck;
+	struct page *p;
+
+	/*
+	 * Strictly check, but there is still a rare case, where both _refcnt and
+	 * _mapcount are forged by some wrong code
+	 */
+	for (; i < cnt; i += 1 << order) {
+		order = folio_order((struct folio *)check);
+		if (PageBuddy(check)) {
+			if (page_count(check) != 0 || total_mapcount(check) != 0)
+				goto fail;
+			if (check->index != 0)
+				goto fail;
+			if (check->lru.next != LIST_POISON1 ||
+			    check->lru.prev != LIST_POISON2)
+			    goto fail;
+
+		} else if (folio_test_anon((struct folio *)check)) {
+			/* check PAGE_MAPPING_ANON bit in mapping */
+			if (!((unsigned long)check->mapping & PAGE_MAPPING_ANON))
+				goto fail;
+			if (page_count(check) == 0)
+				goto fail;
+			if (total_mapcount(check) != page_count(check))
+				goto fail;
+		} else {
+			goto fail;
+		}
+
+		p = pfn_to_page(pfn);
+		for (int j = 0; j < 1 << order; j++)
+			ClearPageReserved(p + j);
+		__free_pages(p, order);
+
+fail:
+		check += 1 << order;
+		pfn += 1 << order;
+	}
+}
+
+void kdump_kernel_reuse_mem(void)
+{
+	u64 size;
+	struct page *wreck;
+	struct kvec kvec;
+	struct iov_iter iter;
+	char *buf;
+
+	if (!is_kdump_kernel())
+		return;
+
+	if (!kdump_cma_pfn || !kdump_cma_pg_cnt || !kdump_cma_pg_paddr)
+		return;
+
+	size = kdump_cma_pg_cnt * sizeof(struct page);
+	/* copy the wreck's page[] */
+	buf = kmalloc(size, GFP_KERNEL);
+	if (!buf)
+		return;
+	wreck = (struct page *)buf;
+	kvec.iov_base = buf;
+	kvec.iov_len = size;
+	iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, size);
+	read_from_oldmem(&iter, size, &kdump_cma_pg_paddr,
+			cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));
+	check_poison_page(wreck, kdump_cma_pg_cnt, kdump_cma_pfn);
+}
-- 
2.31.1


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