Re: Fwd: about page table

[Tim Deegan <tim@xen.org>]

Hello, 

Please read http://wiki.xen.org/xenwiki/AskingXenDevelQuestions before
posting again; it's pretty unclear from your email what you're trying to
do and how it fails.

At 17:16 +0800 on 12 Sep (1315847793), ???? wrote:
> Hi,everyone
> I have been using dbg_pv_va2mfn() function to scan PV dom's page
> table.However,when i intended to modify the page table's entry.Something
> went wrong.
> Should I modify the P2M and M2P table,either?But I kind of lose track of how
> things work at P2M and M2P table.Can someone tell me something about these
> tables.
> Or can someone can tell me which function can come in handy,or where to look
> in.
> I am in the middle of  a project that needs to manipulate the page table in
> dom.

OK, I guess from the code below that you want to change the contents of
a PV guest's pagetables from inside Xen?  That's not really allowed --
since PV guests make their own pagetables you need to have the guest
OS's cooperation.

If you tell us what the project is, and _why_ you want to do this, we
might be able to suggest a better approach. 

Cheers,

Tim.

> For example,
> static unsigned long
> dbg_pv_va2mfn(dbgva_t vaddr, struct domain *dp, uint64_t pgd3val)
> {
>     l3_pgentry_t l3e, *l3t;
>     l2_pgentry_t l2e, *l2t;
>     l1_pgentry_t l1e, *l1t;
>     unsigned long cr3 = (pgd3val ? pgd3val : dp->vcpu[0]->arch.cr3);
>     unsigned long mfn = cr3 >> PAGE_SHIFT;
> 
>     DBGP2("vaddr:%lx domid:%d cr3:%lx pgd3:%lx\n", vaddr, dp->domain_id,
>           cr3, pgd3val);
> 
>     if ( pgd3val == 0 )
>     {
>         l3t  = map_domain_page(mfn);
>         l3t += (cr3 & 0xFE0UL) >> 3;
>         l3e = l3t[l3_table_offset(vaddr)];
>         mfn = l3e_get_pfn(l3e);
>         unmap_domain_page(l3t);
>         if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) )
>             return INVALID_MFN;
>     }
> 
>     l2t = map_domain_page(mfn);
>     l2e = l2t[l2_table_offset(vaddr)];
>     mfn = l2e_get_pfn(l2e);
>     unmap_domain_page(l2t);
>     if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) ||
>          (l2e_get_flags(l2e) & _PAGE_PSE) )
>         return INVALID_MFN;
> 
>     l1t = map_domain_page(mfn);
>     l1e = l1t[l1_table_offset(vaddr)];----------------------------------(1)
>     mfn = l1e_get_pfn(l1e);----------------------------------------------(2)
> 
>     unmap_domain_page(l1t);
> 
>     return mfn_valid(mfn) ? mfn : INVALID_MFN;
> }
> What should i do if i want to change the l1e page table entry.I allocate a
> page using the function alloc_domheap_page,and use l1e_from_page() to write
> the l1e entry,but it proved to be wrong,and my system keeps reboot itself.
> Can anyone gives me a hand?
> 
> 
>                        Thanks

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