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Subject[PATCH v2 2/2] efi: arm64: Introduce /proc/efi/memreserve to tell the persistent pages
Date
From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

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@jp.fujitsu.com>
---
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
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