Re:Re: Re: Re:Re:Re: [Xen-devel] Questions about shadow page table.

["Wu Bingzheng" <wubingzheng@xxxxxxx>]

Thanks so much.

I have another question.

If a process's page is read-write in guest's page table, but the Xen hypervisor sets it as read-only in shadow page table on some purpose. What happens if the process writes this page?
Is this case treated as guest page fault or shadow page fault?

Thanks,
Wu


>At 10:10 +0100 on 27 May (1243419042), Wu Bingzheng wrote:
>> ??2009-05-27??"Tim Deegan" <Tim.Deegan@xxxxxxxxxx> ??????
>> >At 04:09 +0100 on 27 May (1243397391), Wu Bingzheng wrote:
>> >> In another word, how can page-fault handler distinguish the
>> >> shadow-page-fault and non-shadow-page-fault?
>> >
>> >By looking at the guest's own pagetables (not the shadows) and the error
>> >code, and figuring out whether this would have been a pagefault on bare
>> >metal.  Yes, the not_a_shadow_fault path is for this.
>
>Actually, all "goto propagate" paths in sh_page_fault() do this too; the
>not_a_shadow_fault label also has some lock handling that's required on
>some paths.
>
>> Thanks. Would you like to point out where exactly to make the
>> decision?
>
>Typical guest faults are caught at the first "goto propagate", based on
>the return code of sh_walk_guest_tables().
>
>Cheers,
>
>Tim.
>
>-- 
>Tim Deegan <Tim.Deegan@xxxxxxxxxx>
>Principal Software Engineer, Citrix Systems (R&D) Ltd.
>[Company #02300071, SL9 0DZ, UK.]
>
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