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SubjectRE: [RFC PATCH] efi: arm64: Introduce /sys/firmware/efi/memreserve to tell the persistent pages
Date


> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Masayoshi Mizuma
> Sent: Wednesday, November 13, 2019 1:53 AM
> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>;
> linux-arm-kernel@lists.infradead.org; linux-efi@vger.kernel.org
> Cc: Masayoshi Mizuma <msys.mizuma@gmail.com>; Mizuma, Masayoshi/水間 理仁
> <m.mizuma@jp.fujitsu.com>; linux-kernel@vger.kernel.org;
> kexec@lists.infradead.org
> Subject: [RFC PATCH] efi: arm64: Introduce /sys/firmware/efi/memreserve to
> tell the persistent pages
>
> 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;

Other functions use different conditions.
The latter efi_memreserve_root == (void *)ULONG_MAX is correct?

static int __init efi_memreserve_map_root(void)
{
if (efi.mem_reserve == EFI_INVALID_TABLE_ADDR)
return -ENODEV;

int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
{
struct linux_efi_memreserve *rsv;
unsigned long prsv;
int rc, index;

if (efi_memreserve_root == (void *)ULONG_MAX)
return -ENODEV;

> +
> + for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
> + rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);

memremap() could fail with NULL as a return value.
You need to deal with such case.

It looks to me efi_mem_reserve_persistent() also doesn't deal with this.
Maybe you should fix this, too.

> + 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);

Is memreserve supported on 32-bit system?
If so, phy_addr_t could have a type of 4-byte length in such system
(not so if with PAE) and then %llx could lead to inconsistent type error.
It's enough to add a cast to unsigned long long.

> + 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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