Re: [Qemu-devel] [Qemu-trivial] [PATCH] target-i386: fix order of checks in cpu_get_phys_page_debug

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Apr 04, 2013 at 07:13:03PM -0400, Brendan Dolan-Gavitt wrote:
> In target-i386 cpu_get_phys_page_debug, the CR4_PAE bit is checked
> before CR0_PG. This means that if paging is disabled but the PAE bit has
> been set in CR4, cpu_get_phys_page_debug will return the wrong result
> (it will try to translate the address as virtual rather than using it as
> a physical address). This patch fixes that by moving the CR0_PG check to
> the beginning of the function.
> 
> This shows up when booting the Linux kernel on amd64 with "-d in_asm".
> The kernel turns on the PAE bit in CR4 before turning on paging, and so
> QEMU's disassembler will fail because it will try to walk the page
> tables to fetch code even though paging is disabled. The symptom is
> incorrect disassembly and some "Disassembler disagrees with translator
> over instruction decoding" messages.
> 
> This was also reported as bug #1163065.
> 
> Signed-off-by: Brendan Dolan-Gavitt <brendandg@gatech.edu>
> ---
>  target-i386/helper.c |  121 ++++++++++++++++++++++++++------------------------
>  1 file changed, 64 insertions(+), 57 deletions(-)

Sorry, not trivial :).

Stefan