Xen devel - Dec 2006 - Share Memory Between DomainU and Domain0

Hi.

 

I want to share some pages between Dom0 and DomU.

But I have some problems with it. 

 

The sharing scenario is like that.

 

1.     Dom0 grants access permission of pages to DomU  using
"gnttab_grant_foreign_access_ref()"

2.     Dom0 passes "Machine Page Numbers" and "Ref" to DomU
through I/O Ring

3.     DomU install granted pages. (Change original mfn to new mfn of Dom0)

A.     map.host_addr = mfn_to_virt(pfn_to_mfn(DomU''s PFN));

B.      HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,&map,count)

C.      Set_phys_to_machine(DomU''s PFN, Dom0''s MFN)

 

 

They are being done in "blkback.c" and "blkfront.c".

 

The source code is

 

In blkback.c

           dom0_cache_vaddr = get_zeroed_page(GFP_KERNEL);

           dom0_cache_mfn[i] = pfn_to_mfn(__pa(dom0_cache_vaddr) >>
PAGE_SHIFT);

share_ref = gnttab_claim_grant_reference(&share_ref_head);

           BUG_ON(share_ref == -ENOSPC);

           share_ref = gnttab_grant_foreign_access( req_domid,
dom0_cache_mfn[i], 1);

 

In blkfront.c

           bret = RING_GET_RESPONSE(&info->ring, i);

           map.host_addr mfn_to_virt(pfn_to_mfn(bret->map_pfn_mfn[j].pfn));

for(j < 0 ; j < number_of_pages ;j++){

                      map.dom = (domid_t) 0;

                      map.ref = bret->map_pfn_mfn[j].ref;

                      map.flags = ( GNTMAP_host_map | GNTMAP_readonly);

                                          

                      ret
HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,&map,1);

                      BUG_ON(ret);

set_phys_to_machine(

                                bret->map_pfn_mfn[j].pfn,

                                FOREIGN_FRAME((bret->map_pfn_mfn[j].mfn)));

           }

 

For the sharing, I modified response struct. So it has grant ref,
Dom0''s MFN
and DomU''s PFN now.

 

But I encountered Kernel Panic as DomU booted up.

 

Message :

Unable to handle kernel paging request at virtual address c0cff000

 printing eip:

c0148bc1

*pde = ma 1d639067 pa 0116a067

*pte = ma 0db4f061 pa 10b4f061

 

Question :

1.     Should I update Page table with "HYPERVISOR_mmu_update" in DomU
although I call "HYPERVISOR_grant_table_op"??

2.     Anyone can advice to me about this problem? (Anything about the
kernel panic message or mistakes in source code)

 

Thank you very much. :-)

 



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

Hi there!

Have you made any progress with this? I''ve made some comments inline 
below...
>1.     Dom0 grants access permission of pages to DomU  using
>"gnttab_grant_foreign_access_ref()"
> 2. Dom0 passes "Machine Page Numbers" and "Ref" to DomU
through I/O Ring
>3.     DomU install granted pages. (Change original mfn to new mfn of Dom0)
>A.     map.host_addr = mfn_to_virt(pfn_to_mfn(DomU''s PFN));
>B.      HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,&map,count)
>C.      Set_phys_to_machine(DomU''s PFN, Dom0''s MFN)
>In blkback.c
>
>           dom0_cache_vaddr = get_zeroed_page(GFP_KERNEL);
>
>           dom0_cache_mfn[i] = pfn_to_mfn(__pa(dom0_cache_vaddr) >>
>PAGE_SHIFT);
>
>share_ref = gnttab_claim_grant_reference(&share_ref_head);
>
>           BUG_ON(share_ref == -ENOSPC);
>
>           share_ref = gnttab_grant_foreign_access( req_domid,
>dom0_cache_mfn[i], 1);
>
> 
>
>In blkfront.c
>
>           bret = RING_GET_RESPONSE(&info->ring, i);
>
>           map.host_addr
>mfn_to_virt(pfn_to_mfn(bret->map_pfn_mfn[j].pfn));
>
>for(j < 0 ; j < number_of_pages ;j++){
>
>                      map.dom = (domid_t) 0;
>
>                      map.ref = bret->map_pfn_mfn[j].ref;
>
>                      map.flags = ( GNTMAP_host_map | GNTMAP_readonly);
>
>                                          
>
>                      ret
>HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,&map,1);
>
>                      BUG_ON(ret);
>
>set_phys_to_machine(
>
>                                bret->map_pfn_mfn[j].pfn,
>
>                               
FOREIGN_FRAME((bret->map_pfn_mfn[j].mfn)));
>
>           }
>
> 
>
> For the sharing, I modified response struct. So it has grant ref,
Dom0''s
> MFN and DomU''s PFN now.
OK. Make sure your dom0 and domU are *definitely* using the same version of 
the block drivers, and that both kernels are compiled to use your modified 
request structure. Otherwise things will get very confused. If you''re
using
two kernels, make sure you rebuild them both.

How does dom0 know what the domU''s pfn is in order to queue it in
responses?
>But I encountered Kernel Panic as DomU booted up.
<snip>
>Question :
>
>1.     Should I update Page table with "HYPERVISOR_mmu_update" in
DomU
>although I call "HYPERVISOR_grant_table_op"??
That shouldn''t be necessary.
>2.     Anyone can advice to me about this problem? (Anything about the
>kernel panic message or mistakes in source code)
Are you trying to implement a shared buffer cache or something similar? 
Could you possibly post your entire diff vs the standard block drivers so 
that I can take a look at everything in context? I''ve written some
similar
code to this but would like to look through a full diff if possible.

Cheers,
Mark

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel