Fwd: [PATCH] BGRT: Don't ioremap if image address is in System RAM(was: Re: BGRT Pointer in System RAM)

[Parag Warudkar]

On Jul 16, 2013 6:55 PM, "Andy Lutomirski" <luto@xxxxxxxxxxxxxx> wrote:

> > Ok, so I played around with it a bit and the following patch works
> > fine on my system. (I.E. image size is reasonable, cat
> > /sys/firmware/acpi/bgrt/image > img.bmp generates a valid,
> > non-distorted bitmap, which it did before too, btw as despite of the
> > ioremap WARN_ON the ioremap seems to succeed if !(is_ram &&
> > pfn_valid(pfn) && !PageReserved.)
> >
>
> How reliable is this?  That is, is there any guarantee that nothing
> will have overwritten the image in memory before this code runs?
>
>From the little digging I did, this code runs fairly early in the boot
process, right after ACPI acquires all tables. If I am not mistaken it
runs as part of efi_late_init which should be before
efi_free_boot_services() is called.
Image address on my system is  00000000B2E1B018. At boot EFI prints
the following -

[    0.000000] efi: mem23: type=4, attr=0xf,
range=[0x00000000b2c34000-0x00000000b2e5d0

Type=4, again if I am not mistaken is EFI_BOOT_SERVICES_DATA. So all
put together I think it should be reliable to read off of that address
when efi-bgrt-init runs, which is before the boot services code and
data are discarded.

Parag
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/