Re: [Qemu-devel] [PATCH] x86: only allow real mode to access 32bit without LMA

[Richard Henderson <rth@twiddle.net>]

On 12/07/2013 01:52 AM, 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.
> 
> Reported-by: Michael Tokarev <mjt@tls.msk.ru>
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  target-i386/helper.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~