[Xen-ia64-devel] HVM hangs with screen_info patch applied

[Jes Sorensen <jes@xxxxxxx>]

Hi,

Having had a ton of problems booting my self-compiled recent kernels
under KVM, I started tracking down the patch causing the issues. It
looks like it's patch e087db510cd96a75a614f6f6fcd5499ab21cb087 which
simply changes the packing attributes to struct screen_info. Given that
we on ia64 don't have to match the struct to anything passed in by the
boot loader, this really shouldn't matter, but it seems like it does.

I mentioned this on #ia64 and it shows up Alex Williamson hit a similar
problem with HVM emulation under Xen some time ago. However, the problem
went away by itself. Ie. it looks like this could be either a compiler,
qemu or some of the hypervisor code shared by Xen and KVM that causes
the problem. I doubt it's gcc related, given that the code works fine on
real hardware.

The other things I noticed is that the hangs go away if I compile my
guest kernel with gcc 3.4.3, whereas it fails using gcc-4.1.2 and 4.0.2.

Anyway, not a fix, but I wanted to let everyone know that if you are
seeing boot hangs of HVM guests it could be the same problem you are
facing.

Cheers,
Jes



commit e087db510cd96a75a614f6f6fcd5499ab21cb087
Author: H. Peter Anvin <hpa@xxxxxxxxx>
Date:   Wed Jul 11 12:18:31 2007 -0700

    Clean up struct screen_info (<linux/screen_info.h>)

    struct screen_info has unaligned members, it needs to be packed.
    In the process, fix the naming of some of the members, which don't
    belong in this structure but are part of it anyway.

    Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
    Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>


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