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

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Message-ID: <CAOULuOapAGOcKVo5be4jUEFZYQUKv2fBOcMn79U7s0NJHz5Ugw@mail.gmail.com>
Date:	Tue, 16 Jul 2013 19:28:47 -0400
From:	Parag Warudkar <parag.lkml@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org
Subject: Fwd: [PATCH] BGRT: Don't ioremap if image address is in System RAM
 (was: Re: BGRT Pointer in System RAM)

On Jul 16, 2013 6:55 PM, "Andy Lutomirski" <luto@...capital.net> 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
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