From mboxrd@z Thu Jan  1 00:00:00 1970
From: Matt Fleming <matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>
Subject: Re: BGRT doesn't work for me on efi-next
Date: Fri, 18 Dec 2015 12:56:28 +0000
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To: =?iso-8859-1?Q?M=F4she?= van der Sterre <me-A/3C56C7qwM@public.gmane.org>
Cc: Sai Praneeth <sai.praneeth.prakhya-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, Matthew Garrett <mjg59-1xO5oi07KQx4cg9Nei1l7Q@public.gmane.org>, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Juergen Gross <jgross-IBi9RG/b67k@public.gmane.org>
List-Id: linux-efi@vger.kernel.org

(Pulling in Ingo and Juergen because of commit 954e12f7a800)

On Thu, 17 Dec, at 05:30:45PM, M=F4she van der Sterre wrote:
> Hello Sai and others,
>=20
> The change to use early_mem*() instead of early_io*() in 50a0cb56 doe=
s not
> work on my machine. Last week I discussed some BGRT changes and I cre=
ated a
> patch for that, but can't test it on efi-next because of this.
>=20
> I get this (when booting 50a0cb56, without any of my changes):
> [    0.026936] ------------[ cut here ]------------
> [    0.026941] WARNING: CPU: 0 PID: 0 at mm/early_ioremap.c:137
> __early_ioremap+0x102/0x1bb()
> [    0.026941] Modules linked in:
> [    0.026944] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc1 #2
> [    0.026945] Hardware name: Dell Inc. XPS 13 9343/09K8G1, BIOS A05
> 07/14/2015
> [    0.026946]  0000000000000000 900f03d5a116524d ffffffff81c03e60
> ffffffff813a3fff
> [    0.026948]  0000000000000000 ffffffff81c03e98 ffffffff810a0852
> 00000000d7b76000
> [    0.026949]  0000000000000000 0000000000000001 0000000000000001
> 000000000000017c
> [    0.026951] Call Trace:
> [    0.026955]  [<ffffffff813a3fff>] dump_stack+0x44/0x55
> [    0.026958]  [<ffffffff810a0852>] warn_slowpath_common+0x82/0xc0
> [    0.026959]  [<ffffffff810a099a>] warn_slowpath_null+0x1a/0x20
> [    0.026961]  [<ffffffff81d8c395>] __early_ioremap+0x102/0x1bb
> [    0.026962]  [<ffffffff81d8c602>] early_memremap+0x13/0x15
> [    0.026964]  [<ffffffff81d78361>] efi_bgrt_init+0x162/0x1ad
> [    0.026966]  [<ffffffff81d778ec>] efi_late_init+0x9/0xb
> [    0.026968]  [<ffffffff81d58ff5>] start_kernel+0x46f/0x49f
> [    0.026970]  [<ffffffff81d58120>] ? early_idt_handler_array+0x120/=
0x120
> [    0.026972]  [<ffffffff81d58339>] x86_64_start_reservations+0x2a/0=
x2c
> [    0.026974]  [<ffffffff81d58485>] x86_64_start_kernel+0x14a/0x16d
> [    0.026977] ---[ end trace f9b3812eb8e24c58 ]---
> [    0.026978] efi_bgrt: Ignoring BGRT: failed to map image memory
>=20
> This is the second early_memremap call in efi_bgrt_init triggering
> WARN_ON(nrpages > NR_FIX_BTMAPS). Can you comment on this?

Hmm... yeah NR_FIX_BTMAPS =3D=3D 64, so early_memremap() is limited to
mapping ~200KB at once. That's not very big, your BGRT data is likely
much larger than that.

Obviously we can't use efi_lookup_mapped_addr() any more, so it makes
sense to come up with a much robust way to memremap the BGRT image.

The immediate solution that comes to mind is using memremap() instead
of the early_* version, since the late version won't use the FIXMAP
area and will allow us to map a much larger region into the kernel
virtual address space.

Digging through the history it appears I was the one who made the
switch from ioremap() to early_memremap() in commit 081cd62a010f
("x86/efi: Allow mapping BGRT on x86-32"), which I suspect was because
a generic memremap() implementation didn't exist at the time. Dan
Williams introduced one in Aug 2015 with commit 92281dee825f ("arch:
introduce memremap()").

Somewhat surprisingly, Juergen switched the BGRT driver from
early_memremap() to early_ioremap() in commit 954e12f7a800 ("x86/mm,
efi: Use early_ioremap() in arch/x86/platform/efi/efi-bgrt.c")
although I can't figure out why because this isn't I/O memory. And now
we're attempting to switch it back.

Juergen, could you provide a rationale for commit 954e12f7a800? All
the commit message says is that it's "an I/O-area", but that isn't
true.

In the meantime M=F4she, could you try this patch ontop of the EFI
'next' branch? (Note it may not work/compile, but you get the gist)

---

diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/e=
fi-bgrt.c
index bf51f4c02562..b0970661870a 100644
--- a/arch/x86/platform/efi/efi-bgrt.c
+++ b/arch/x86/platform/efi/efi-bgrt.c
@@ -72,14 +72,14 @@ void __init efi_bgrt_init(void)
 		return;
 	}
=20
-	image =3D early_memremap(bgrt_tab->image_address, sizeof(bmp_header))=
;
+	image =3D memremap(bgrt_tab->image_address, sizeof(bmp_header), MEMRE=
MAP_WB);
 	if (!image) {
 		pr_err("Ignoring BGRT: failed to map image header memory\n");
 		return;
 	}
=20
 	memcpy(&bmp_header, image, sizeof(bmp_header));
-	early_memunmap(image, sizeof(bmp_header));
+	memunmap(image);
 	bgrt_image_size =3D bmp_header.size;
=20
 	bgrt_image =3D kmalloc(bgrt_image_size, GFP_KERNEL | __GFP_NOWARN);
@@ -89,7 +89,7 @@ void __init efi_bgrt_init(void)
 		return;
 	}
=20
-	image =3D early_memremap(bgrt_tab->image_address, bmp_header.size);
+	image =3D memremap(bgrt_tab->image_address, bmp_header.size, MEMREMAP=
_WB);
 	if (!image) {
 		pr_err("Ignoring BGRT: failed to map image memory\n");
 		kfree(bgrt_image);
@@ -98,5 +98,5 @@ void __init efi_bgrt_init(void)
 	}
=20
 	memcpy(bgrt_image, image, bgrt_image_size);
-	early_memunmap(image, bmp_header.size);
+	memunmap(image);
 }