Messages in this thread |  | | | Subject | Re: [PATCH v5 10/10] x86, efi: EFI boot stub support | | From | Matt Fleming <> | | Date | Thu, 24 Nov 2011 20:56:56 +0000 |
| |
On Thu, 2011-11-24 at 15:43 +0100, Maarten Lankhorst wrote: > Hey Matt, > > On 11/23/2011 08:27 PM, Matt Fleming wrote: > > > On Wed, 2011-11-23 at 01:44 +0100, Maarten Lankhorst wrote: > >> When I tested this with v3.2-rc2 it didn't boot, it hung before it > >> initialized the kernel. > >> Without initrd it works fine, though. > > Bah, so this change actually makes booting worse? You said before that > > you almost made it to userspace but this seems to hang much earlier now. > > Is that correct? > > > > ... back to the drawing board. > I was looking at why grub2 could boot, seems to be it reads in chunks of > 256 kilobytes. I seem to be able to get it to boot with chunks of 4 mb > as well, but didn't test beyond that. > > So the fix is to simply read the file in parts, otherwise efi hangs.. > As a nice side effect, short reads are also handled, but the efi > firmware seems to choke over huge reads and dies.
Urrggghh..... Thanks a lot for diagnosing this, Maarten! The copy of grub that I have (fedora's version) looks like it uses the disk_io protocol to read from disks, I wonder if there's a reason for this. I Cc'd Peter Jones in case he's seen anything like this before.
Aha, read_file() in the elilo source contains this helpful comment,
/* * We load by chunks rather than a single big read because * early versions of EFI had troubles loading files * from floppies in a single big request. Breaking * the read down into chunks of 4KB fixed that * problem. While this problem has been fixed, we still prefer * this method because it tells us whether or not we're making * forward progress. */ (but reading the code it's clear it uses a chunk size of 16KB, not 4KB)
So, it looks like it's not just reading from floppies that hits this bug in the firmware.
Maarten, could you send a patch against the 'x86/efi-stub' branch at git://git.kernel.org/pub/scm/linux/kernel/git/mfleming/linux.git that splits the read up into 16KB chunks and explains,
- why we need to do the reading in chunks - why we chose the 16KB chunk size (because elilo said so)
That way, the bug fix will be properly documented and attributed to you.
-- Matt Fleming, Intel Open Source Technology Center
|  |