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


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH for-2.0?] target-i386: fix gdb debugging with large memory guests
Date: Tue, 18 Mar 2014 17:37:23 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

Il 18/03/2014 17:23, Luiz Capitulino ha scritto:
On Tue, 18 Mar 2014 15:36:45 +0100
Jan Kiszka <address@hidden> 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?

You only need to move the new code into the "if (env->hflags & HF_LMA_MASK)", I think. The subject is ok.

Paolo




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