Re: [Qemu-devel] [PATCH for-2.0?] target-i386: fix gdb debugging with large memory guests

[Luiz Capitulino <lcapitulino@redhat.com>]

On Tue, 18 Mar 2014 15:36:45 +0100
Jan Kiszka <jan.kiszka@siemens.com> wrote:

> >> Right, this belongs in the "if (env->hflags & HF_LMA_MASK)" block.
> >>
> >> And the subject or description should mention that
> >> x86_cpu_get_phys_page_debug was lacking support for 1G hugepages.
> > 
> > To be honest, although the PS bit is set and that indicates a 1GB page,
> > I didn't know Linux does that. I thought Linux would use 4KB pages for
> > everything unless it's explicitly asked to use bigger pages. Also, note that
> > I was using gdb to debug really early kernel boot code (start_kernel()).
> 
> I could imagine that Linux initially creates a giant identity mapping
> page table for the startup process and only later on switches to
> fine-grained tables of 4K and 2M pages. Giant pages still require
> hughtlbfs, IIRC.
> 
> > 
> > I'd feel more confident to have such a changelog after I find out where
> > exactly Linux sets that bit, but I won't have time in the next days. On the
> > other hand, the patch does fix the problem to me.
> 
> Don't worry about Linux (the code should work with any OS anyway), just
> believe your reviewers. ;) Alternatively, check Intel IA32 SDM on page
> table structures.

OK, so you want me to change the subject? Anything else for v2?