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Re: [Qemu-trivial] [PATCH] x86: only allow real mode to access 32bit wit


From: Michael Tokarev
Subject: Re: [Qemu-trivial] [PATCH] x86: only allow real mode to access 32bit without LMA
Date: Sat, 07 Dec 2013 22:49:06 +0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131103 Icedove/17.0.10

06.12.2013 16:52, Alexander Graf wrote:
> When we're running in non-64bit mode with qemu-system-x86_64 we can
> still end up with virtual addresses that are above the 32bit boundary
> if a segment offset is set up.
> 
> GNU Hurd does exactly that. It sets the segment offset to 0x80000000 and
> puts its EIP value to 0x8xxxxxxx to access low memory.
> 
> This doesn't hit us when we enable paging, as there we just mask away the
> unused bits. But with real mode, we assume that vaddr == paddr which is
> wrong in this case. Real hardware wraps the virtual address around at the
> 32bit boundary. So let's do the same.
> 
> This fixes booting GNU Hurd in qemu-system-x86_64 for me.

Since i386 tcg code has no active maintainer and since this is a rather
simple change, I'll queue it up to trivial-patches.

Thank you!

/mjt



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