Xen devel - Nov 2006 - RE: [Patch] Fix for x86_64 boot failures due tobadsegment setup for protected mode.

This cause problem for some version''s SMP windows, at least 2003 64-bit
smp windows AP bringup code has such issue.
I''m not sure how much decoder left if we want to do full emulation. But
at least we need to add the "mov reg->sreg" as Keir pointed out.
It''s very later on my side, so Stephen, would you please add this?

Thanks
Yunhong Jiang
-----Original Message-----
From: Stephen C. Tweedie [mailto:sct@redhat.com] 
Sent: 2006年11月11日 0:09
To: Jiang, Yunhong
Cc: Keir Fraser; Yu, Wilfred; Xin, Xiaohui; xen-devel@lists.xensource.com;
Herbert Xu; Li, Susie; Steven Rostedt; Li, Xin B; Stephen Tweedie
Subject: RE: [Xen-devel] [Patch] Fix for x86_64 boot failures due tobadsegment
setup for protected mode.

Hi,

On Fri, 2006-11-10 at 22:39 +0800, Jiang, Yunhong wrote:
> This patch caused one problem.
> 
> If the guest change the DS/SS etc between it set cr0.PE and the jump
instruction.
Hmm...  Do you know how much of a problem that causes in practice?
Which guests have that behaviour?
> Considering following code:
>    mov eax, cr0
>    or eax, 0x11
>   mov cr0, eax		---> here enable PE, and old_ctx.ds is cleard
>    mov ax, 0x0020
>    mov ds, ax		-> changes the DS here
Well, we''ve got commit log comments for the "pop %es" case:

2) In
current vmxassist, when entering VM86_PROTECTED_TO_REAL, we need to
decode every instruction manually until we catch instructions like
jmpl to reset cs to really return to real mode.

So I''m afraid I just assumed that we wouldn''t need to deal
with ds in
real life, since we haven''t added emulation for that so far.  Is that
emulation we need to add as a matter of some urgency, then?

--Stephen

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I have a patch I''ll check in. It''d be good get some testing of
it.

Changeset is 12365:ca75b51d69c7

 -- Keir


On 10/11/06 17:04, "Jiang, Yunhong" <yunhong.jiang@intel.com>
wrote:
> This cause problem for some version''s SMP windows, at least 2003
64-bit smp
> windows AP bringup code has such issue.
> I''m not sure how much decoder left if we want to do full
emulation. But at
> least we need to add the "mov reg->sreg" as Keir pointed out.
> It''s very later on my side, so Stephen, would you please add this?
> 
> Thanks
> Yunhong Jiang
> -----Original Message-----
> From: Stephen C. Tweedie [mailto:sct@redhat.com]
> Sent: 2006年11月11日 0:09
> To: Jiang, Yunhong
> Cc: Keir Fraser; Yu, Wilfred; Xin, Xiaohui; xen-devel@lists.xensource.com;
> Herbert Xu; Li, Susie; Steven Rostedt; Li, Xin B; Stephen Tweedie
> Subject: RE: [Xen-devel] [Patch] Fix for x86_64 boot failures due
tobadsegment
> setup for protected mode.
> 
> Hi,
> 
> On Fri, 2006-11-10 at 22:39 +0800, Jiang, Yunhong wrote:
>> This patch caused one problem.
>> 
>> If the guest change the DS/SS etc between it set cr0.PE and the jump
>> instruction.
> 
> Hmm...  Do you know how much of a problem that causes in practice?
> Which guests have that behaviour?
> 
>> Considering following code:
>>    mov eax, cr0
>>    or eax, 0x11
>>   mov cr0, eax  ---> here enable PE, and old_ctx.ds is cleard
>>    mov ax, 0x0020
>>    mov ds, ax  -> changes the DS here
> 
> Well, we''ve got commit log comments for the "pop %es"
case:
> 
> 2) In
> current vmxassist, when entering VM86_PROTECTED_TO_REAL, we need to
> decode every instruction manually until we catch instructions like
> jmpl to reset cs to really return to real mode.
> 
> So I''m afraid I just assumed that we wouldn''t need to
deal with ds in
> real life, since we haven''t added emulation for that so far.  Is
that
> emulation we need to add as a matter of some urgency, then?
> 
> --Stephen
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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Keir Fraser wrote:
> I have a patch I''ll check in. It''d be good get some
testing of it.
> 
> Changeset is 12365:ca75b51d69c7
> 
>  -- Keir
> 
Keir,

I was playing with Plan9 which happens to also tinker with ss, fs, and
gs in this critical section. It still crashes pretty early, but it
crashes earlier without this patch.  This patch lets Plan9 crash at the
same location before the original patch Stephen Tweedie sent :}.

This patch makes the mov_to_seg more complete. I left out cs, since I
don''t think that would even make sense with a mov.

-- Steve

Signed-off-by: Steven Rostedt <srostedt@redhat.com>




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On 10/11/06 10:32 pm, "Steven Rostedt" <srostedt@redhat.com>
wrote:
> I was playing with Plan9 which happens to also tinker with ss, fs, and
> gs in this critical section. It still crashes pretty early, but it
> crashes earlier without this patch.  This patch lets Plan9 crash at the
> same location before the original patch Stephen Tweedie sent :}.
> 
> This patch makes the mov_to_seg more complete. I left out cs, since I
> don''t think that would even make sense with a mov.
Thanks, I''ll check this in.

 -- Keir


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