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Subject[RFC PATCH] efi: arm64: Introduce /sys/firmware/efi/memreserve to tell the persistent pages
Date
From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

kexec reboot stucks because efi_config_parse_tables() refers garbage
(with memblock=debug):

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 pending table and prop table which are allocated by gic_reserve_range().

The destroyer is kexec. kexec locates the inird 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:
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 appropriate 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 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@jp.fujitsu.com>
---
drivers/firmware/efi/efi.c | 32 +++++++++++++++++++++++++++++++-
1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index e98bbf8e5..67b21ae7a 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -141,6 +141,36 @@ 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;
+static ssize_t memreserve_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct linux_efi_memreserve *rsv;
+ unsigned long prsv;
+ char *str = buf;
+ int index, i;
+
+ if (!kobj || !buf)
+ return -EINVAL;
+
+ if (!efi_memreserve_root)
+ return -ENODEV;
+
+ for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
+ rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
+ index = atomic_read(&rsv->count);
+ for (i = 0; i < index; i++)
+ str += sprintf(str, "%llx-%llx\n",
+ rsv->entry[i].base,
+ rsv->entry[i].base + rsv->entry[i].size - 1);
+ memunmap(rsv);
+ }
+
+ return str - buf;
+}
+
+static struct kobj_attribute efi_attr_memreserve = __ATTR_RO_MODE(memreserve, 0444);
+
#define EFI_FIELD(var) efi.var

#define EFI_ATTR_SHOW(name) \
@@ -172,6 +202,7 @@ static struct attribute *efi_subsys_attrs[] = {
&efi_attr_runtime.attr,
&efi_attr_config_table.attr,
&efi_attr_fw_platform_size.attr,
+ &efi_attr_memreserve.attr,
NULL,
};

@@ -955,7 +986,6 @@ 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
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