[PATCH v2 2/2] efi: arm64: Introduce /proc/efi/memreserve to tell the persistent pages

[Masayoshi Mizuma]

From: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

kexec reboot stops in early boot sequence because efi_config_parse_tables()
refers garbage data. We can see the log with memblock=debug kernel option:

  efi:  ACPI 2.0=0x9821790014  PROP=0x8757f5c0  SMBIOS 3.0=0x9820740000  MEMRESERVE=0x9820bfdc58
  memblock_reserve: [0x0000009820bfdc58-0x0000009820bfdc67] efi_config_parse_tables+0x228/0x278
  memblock_reserve: [0x0000000082760000-0x00000000324d07ff] efi_config_parse_tables+0x228/0x278
  memblock_reserve: [0xcc4f84ecc0511670-0x5f6e5214a7fd91f9] efi_config_parse_tables+0x244/0x278
  memblock_reserve: [0xd2fd4144b9af693d-0xad0c1db1086f40a2] efi_config_parse_tables+0x244/0x278
  memblock_reserve: [0x0c719bb159b1fadc-0x5aa6e62a1417ce12] efi_config_parse_tables+0x244/0x278
  ...

That happens because 0x82760000, struct linux_efi_memreserve, is destroyed.
0x82760000 is pointed from efi.mem_reseve, and efi.mem_reserve points the
head page of LPI pending table and LPI property table which are allocated by
gic_reserve_range().

The destroyer is kexec. kexec locates the initrd to the area:

  ]# kexec -d -l /boot/vmlinuz-5.4.0-rc7 /boot/initramfs-5.4.0-rc7.img --reuse-cmdline
  ...
  initrd: base 82290000, size 388dd8ah (59301258)
  ...

>From dynamic debug log. initrd is located in segment[1]:
  machine_kexec_prepare:70:
    kexec kimage info:
      type:        0
      start:       85b30680
      head:        0
      nr_segments: 4
        segment[0]: 0000000080480000 - 0000000082290000, 0x1e10000 bytes, 481 pages
        segment[1]: 0000000082290000 - 0000000085b20000, 0x3890000 bytes, 905 pages
        segment[2]: 0000000085b20000 - 0000000085b30000, 0x10000 bytes, 1 pages
        segment[3]: 0000000085b30000 - 0000000085b40000, 0x10000 bytes, 1 pages

kexec searches the memory region to locate initrd through
"System RAM" in /proc/iomem. The pending tables are included in
"System RAM" because they are allocated by alloc_pages(), so kexec
destroys the LPI pending tables.

Introduce /proc/efi/memreserve to tell the pages pointed by
efi.mem_reserve so that kexec can avoid the area to locate initrd.

Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
---
 drivers/firmware/efi/efi.c | 75 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 72 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index d8157cb34..80bbe0b3e 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -325,17 +325,87 @@ static __init int efivar_ssdt_load(void)
 static inline int efivar_ssdt_load(void) { return 0; }
 #endif
 
+static struct linux_efi_memreserve *efi_memreserve_root __ro_after_init;
+
 #ifdef CONFIG_PROC_FS
 static struct proc_dir_entry *proc_efi;
+#ifdef CONFIG_KEXEC
+static int memreserve_show(struct seq_file *m, void *v)
+{
+	struct linux_efi_memreserve *rsv;
+	phys_addr_t start, end;
+	unsigned long prsv;
+	int count, i;
+
+	if ((efi_memreserve_root == (void *)ULONG_MAX) ||
+			(!efi_memreserve_root))
+		return -ENODEV;
+
+	for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
+		rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
+		if (!rsv) {
+			pr_err("Could not map efi_memreserve\n");
+			return -ENOMEM;
+		}
+		count = atomic_read(&rsv->count);
+		for (i = 0; i < count; i++) {
+			start = rsv->entry[i].base;
+			end = start + rsv->entry[i].size - 1;
+
+			seq_printf(m, "%pa-%pa\n", &start, &end);
+		}
+		memunmap(rsv);
+	}
+
+	return 0;
+}
+
+static int memreserve_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, memreserve_show, NULL);
+}
+
+static const struct file_operations memreserve_fops = {
+	.owner		= THIS_MODULE,
+	.open		= memreserve_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int __init efi_proc_memreserve(void)
+{
+	struct proc_dir_entry *pde;
+
+	if ((efi_memreserve_root == (void *)ULONG_MAX) ||
+			(!efi_memreserve_root))
+		return 0;
+
+	pde = proc_create("memreserve", 0444, proc_efi, &memreserve_fops);
+	if (!pde) {
+		pr_err("/proc/efi: Cannot create /proc/efi/memreserve file.\n");
+		return 1;
+	}
+
+	return 0;
+}
+#else
+static inline int efi_proc_memreserve(void) { return 0; }
+#endif /* CONFIG_KEXEC */
+
 static int __init efi_proc_init(void)
 {
+	int error = 1;
+
 	proc_efi = proc_mkdir("efi", NULL);
 	if (!proc_efi) {
 		pr_err("/proc/efi: Cannot create /proc/efi directroy.\n");
-		return 1;
+		return error;
 	}
 
-	return 0;
+	error = efi_proc_memreserve();
+
+	return error;
 }
 #else
 static inline int efi_proc_init(void) { return 0; }
@@ -986,7 +1056,6 @@ int efi_status_to_err(efi_status_t status)
 }
 
 static DEFINE_SPINLOCK(efi_mem_reserve_persistent_lock);
-static struct linux_efi_memreserve *efi_memreserve_root __ro_after_init;
 
 static int __init efi_memreserve_map_root(void)
 {
-- 
2.18.1