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

[Keir Fraser <keir@xxxxxxxxxxxxx>]

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@xxxxxxxxx> 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@xxxxxxxxxx]
> Sent: 2006年11月11日 0:09
> To: Jiang, Yunhong
> Cc: Keir Fraser; Yu, Wilfred; Xin, Xiaohui; xen-devel@xxxxxxxxxxxxxxxxxxx;
> 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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