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SubjectRe: [PATCH] efi: arm64: Introduce /sys/firmware/efi/memreserve to tell the persistent pages
On Fri, Nov 29, 2019 at 01:25:36PM +0100, Matthias Brugger wrote:
>
>
> On 25/11/2019 19:49, Masayoshi Mizuma wrote:
> > 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.
> >
>
> Doesn't that mean that you haven't enough memory reserved so that you have to
> fallback to allocate it via __get_free_page()?

That's a not fallback allocation. The pending tables and also property
tables are allocated by alloc_pages() on its_allocate_prop_table() and
its_allocate_pending_table().

>
>
> > Introduce /sys/firmware/efi/memreserve to tell the pages pointed by
> > efi.mem_reserve so that kexec can avoid the area to locate initrd.
> >
>
> Doesn't that need a patch for kexec-tools to actually take this into account?

Yes, we need a patch for kexec-tools as well. I'm preparing the kexec
patch.

>
> > Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> > ---
> > 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);
>
> What happens if we provide a buf which is too small?

Good point.
The strings may exceed the buffer size (PAGE_SIZE) in case
efi_memreserve_root has a lot of entries.
It might be better to use seq_printf() to show efi_memreserve_root...
I'll move the file from a sysfs entry to a proc entry so that
efi_memreserve_root can be handled by seq_printf().

Thanks,
Masa

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