RE: [bug #36532] boot in EFI mode (x86_64) fails on some systems

[Stuart_Hayes]

> > > > Vladimir,
> > > >
> > > > The 2.00rc1 version of grub2 still doesn't fix the efi memory map
> > > buffer size I've been working on (though I can see you are now
> > > allocating the efi memory map buffer very shortly before you are
> > > calling grub_efi_finish_boot_services()).
> > > >
> > > > Increasing the mmap_size in find_efi_mmap_size()--as in the patch
> > > immediately above this text--does fix the problem.  Even adding (2
> <<
> > > 12) (instead of (1 << 12)) to the mmap_size will work on the system
> > I'm
> > > testing with.
> > > >
> > >
> > > I've changed it to 3. Thanks. It's annoying that even such simple
> > > operations as we have between find_efi_mmap and finish drastically
> > > increase memory map size.
> > >
> > > --
> > > Regards
> > > Vladimir 'φ-coder/phcoder' Serbinenko
> >
> > Thanks!  I completely agree that it is annoying.
> >
> 
> FYI, while grub-2.00 works on my system now, someone else here at Dell
> has tested it and found that it still doesn't work.  (I verified that
> they were indeed using version 2.00, and saw the error myself).
> 
> I have no idea how or why the memory map size is growing that much.  As
> I get time, I'll try to figure that out...

FYI again:

I've found the problem.  The memory map is not growing wildly... it is more of 
a firmware "quirk."  The firmware is thinking it needs a larger buffer than it 
actually needs.  So calls to GetMemoryMap with a buffer that is smaller than 
(say) 52368 bytes will return EFI_BUFFER_TOO_SMALL and say that the buffer 
needs to be 52368 bytes, but then when you call it with a buffer that's 52368 
bytes, it will put the memory map into the buffer and tell you that the memory 
map is in fact only (say) 24576 bytes.

Unfortunately, right now, find_efi_mmap_size() will then return 24576 bytes 
(plus 3 pages, aligned to a page size), which isn't enough, but not because the 
memory map size is growing...

I'll send in a patch for grub that will make it immune to this quirk... it 
should be pretty low risk (I'm thinking modify find_efi_mmap_size() to use the 
value of mmap_size that was passed to grub_efi_get_memory_map(), rather than 
the value of mmap_size that was returned from that function.)  With that, I 
don't believe it would even need to add 3 pages to the memory map size (I 
watched the memory map size, and it is not growing significantly).

Stuart