[PATCH v2 1/2] efi: esrt: use memremap not ioremap to access ESRT table in memory

[Ard Biesheuvel]

On 18 February 2016 at 14:43, Matt Fleming <matt at codeblueprint.co.uk> wrote:
> On Thu, 18 Feb, at 02:29:32PM, Ard Biesheuvel wrote:
>> On 18 February 2016 at 14:28, Matt Fleming <matt at codeblueprint.co.uk> wrote:
>> > On Thu, 18 Feb, at 01:16:05PM, Ard Biesheuvel wrote:
>> >> On 18 February 2016 at 11:44, Matt Fleming <matt at codeblueprint.co.uk> wrote:
>> >> > On Mon, 15 Feb, at 12:32:32PM, Ard Biesheuvel wrote:
>> >> >> On ARM and arm64, ioremap() and memremap() are not interchangeable like
>> >> >> on x86, and the use of ioremap() on ordinary RAM is typically flagged
>> >> >> as an error if the memory region being mapped is also covered by the
>> >> >> linear mapping, since that would lead to aliases with conflicting
>> >> >> cacheability attributes.
>> >> >>
>> >> >> Since what we are dealing with is not an I/O region with side effects,
>> >> >> using ioremap() here is arguably incorrect anyway, so let's replace
>> >> >> it with memremap instead. Also add a missing unmap on the success path,
>> >> >> and drop a memblock_remove() call which does not belong here, this far
>> >> >> into the boot sequence.
>> >> >>
>> >> >> Cc: Peter Jones <pjones at redhat.com>
>> >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> >> >> ---
>> >> >>  drivers/firmware/efi/esrt.c | 16 ++++++++--------
>> >> >>  1 file changed, 8 insertions(+), 8 deletions(-)
>> >> >>
>> >> >
>> >> > [...]
>> >> >
>> >> >> @@ -432,8 +434,6 @@ static int __init esrt_sysfs_init(void)
>> >> >>       if (error)
>> >> >>               goto err_cleanup_list;
>> >> >>
>> >> >> -     memblock_remove(esrt_data, esrt_data_size);
>> >> >> -
>> >> >>       pr_debug("esrt-sysfs: loaded.\n");
>> >> >>
>> >> >>       return 0;
>> >> >
>> >> > Shouldn't we be replacing memblock_remove() with free_bootmem_late()?
>> >> > The original ESRT region is still reserved at this point, so we should
>> >> > do our best to release it to the page allocator.
>> >>
>> >> I'd rather we keep it reserved. That way, the config table entry still
>> >> points to something valid, which could be useful for kexec(), I think?
>> >> At least, that is how I intended to handle config tables on ARM ...
>> >
>> > If we're going to reserve it why do we need to copy the data out at
>> > all in esrt_sysfs_init()?
>>
>> Excellent question. I don't think there is any point to doing that.
>
> ... Unless the data is contained in an EFI Boot Services region ;-)
>
> Peter?

Yes, it usually is. Is that a problem?