linux-kernel - Re: BGRT Pointer in System RAM

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Message-ID: <20130715230418.GA2649@leaf>
Date:	Mon, 15 Jul 2013 16:04:18 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Parag Warudkar <parag.lkml@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org
Subject: Re: BGRT Pointer in System RAM

On Mon, Jul 15, 2013 at 01:28:36PM -0700, Andy Lutomirski wrote:
> On Sun, Jul 14, 2013 at 12:07 PM, Parag Warudkar <parag.lkml@...il.com> wrote:
> > Saw this warning running latest git (Ubuntu daily mainline.) It looked
> > similar to what Andy saw on MSI hardware -
> > http://www.spinics.net/lists/linux-acpi/msg43410.html . The patch for
> > it doesn't seem to be merged, although it won't help in my case -
> > different hardware with valid status instead of invalid and image
> > address falling in system RAM instead of just being wild.
> >
> > Unsure  how this should be handled - moving the is_ram() check in
> > efi_bgrt_init and ignoring the BGRT in case where the check succeeds?
> > Doesn't sound completely right to me - since the BGRT is valid and
> > exists somewhere, but..
> >
> > [    0.015141] ------------[ cut here ]------------
> > [    0.015147] WARNING: CPU: 0 PID: 0 at
> > /home/apw/COD/linux/arch/x86/mm/ioremap.c:102
> > __ioremap_caller+0x312/0x390()
> > [ snip ]
> > [    0.015160] Call Trace:
> > [    0.015165]  [<ffffffff8170a704>] dump_stack+0x46/0x58
> > [    0.015169]  [<ffffffff8106406c>] warn_slowpath_common+0x8c/0xc0
> > [    0.015171]  [<ffffffff810640ba>] warn_slowpath_null+0x1a/0x20
> > [    0.015173]  [<ffffffff81054e32>] __ioremap_caller+0x312/0x390
> > [    0.015176]  [<ffffffff814013d4>] ? acpi_tb_verify_table+0x54/0x58
> > [    0.015179]  [<ffffffff81d35551>] ? efi_bgrt_init+0x8f/0x143
> > [    0.015181]  [<ffffffff81054f07>] ioremap_nocache+0x17/0x20
> > [    0.015183]  [<ffffffff81d35551>] efi_bgrt_init+0x8f/0x143
> > [    0.015186]  [<ffffffff81401d36>] ? acpi_tb_initialize_facs+0x32/0x34
> > [    0.015188]  [<ffffffff81d34e7f>] efi_late_init+0x9/0xb
> > [    0.015190]  [<ffffffff81d18f17>] start_kernel+0x3fd/0x419
> > [    0.015192]  [<ffffffff81d189ac>] ? do_early_param+0x87/0x87
> > [    0.015194]  [<ffffffff81d18120>] ? early_idt_handlers+0x120/0x120
> > [    0.015196]  [<ffffffff81d185e6>] x86_64_start_reservations+0x2a/0x2c
> >
> > ioremap.c:102
> >     /*
> >          * Don't allow anybody to remap normal RAM that we're using..
> >          */
> >         last_pfn = last_addr >> PAGE_SHIFT;
> >         for (pfn = phys_addr >> PAGE_SHIFT; pfn <= last_pfn; pfn++) {
> >                 int is_ram = page_is_ram(pfn);
> >
> >                 if (is_ram && pfn_valid(pfn) && !PageReserved(pfn_to_page(pfn)))
> >                         return NULL;
> >                 WARN_ON_ONCE(is_ram);
> >         }
> >
> > Looking at the BGRT table from IASL, the status seems to be valid but
> > the image address *seems* to me that is falling under system RAM.
> 
> Interesting.  My BGRT says:
> 
> [028h 0040   8]                Image Address : 0D06801800000001
> 
> If I reverse the high and low 32-bit dwords, then I get an address in
> system RAM.

Does that address in RAM start with a BMP header?

Because that would be *special*.  I don't think it's worth trying to
cope with that bug; better to just write off the BGRT as invalid if the
BIOS can't get endianness right.

In theory we could guess at that bug if the unmangled address points to
a location in RAM starting with a BMP header.  In practice, let's not; a
missing BGRT is a purely cosmetic issue, and BIOS vendors can learn to
get that one right if they want to see their logo during Linux boot.
This won't break fastboot support, it just breaks fancy crossfades from
the BIOS logo to a Linux desktop or splash.

So, a "firmware bug" message in dmesg seems sufficent for that case.  We
do need to handle the case of a valid pointer into memory that e820
calls system RAM, as well as the case of a valid pointer into memory
reserved for the BIOS or similar, but not the case of an invalid
pointer.

- Josh Triplett
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