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

[Masayoshi Mizuma]

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@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.
> > 
> 
> 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@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);
> 
> 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