[PATCH] efi: arm64: Introduce /sys/firmware/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 /sys/firmware/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 | 45 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index e98bbf8e5..0aa07cc09 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -141,6 +141,47 @@ static ssize_t systab_show(struct kobject *kobj,
 
 static struct kobj_attribute efi_attr_systab = __ATTR_RO_MODE(systab, 0400);
 
+static struct linux_efi_memreserve *efi_memreserve_root __ro_after_init;
+#ifdef CONFIG_KEXEC
+static ssize_t memreserve_show(struct kobject *kobj,
+			   struct kobj_attribute *attr, char *buf)
+{
+	struct linux_efi_memreserve *rsv;
+	phys_addr_t start, end;
+	unsigned long prsv;
+	char *str = buf;
+	int count, i;
+
+	if (!kobj || !buf)
+		return -EINVAL;
+
+	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;
+
+			str += sprintf(str, "%pa-%pa\n", &start, &end);
+		}
+		memunmap(rsv);
+	}
+
+	return str - buf;
+}
+
+static struct kobj_attribute efi_attr_memreserve =
+			__ATTR_RO_MODE(memreserve, 0444);
+#endif /* CONFIG_KEXEC */
+
 #define EFI_FIELD(var) efi.var
 
 #define EFI_ATTR_SHOW(name) \
@@ -172,6 +213,9 @@ static struct attribute *efi_subsys_attrs[] = {
 	&efi_attr_runtime.attr,
 	&efi_attr_config_table.attr,
 	&efi_attr_fw_platform_size.attr,
+#ifdef CONFIG_KEXEC
+	&efi_attr_memreserve.attr,
+#endif
 	NULL,
 };
 
@@ -955,7 +999,6 @@ 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