Re: [hybrid]: code review for function mapping pfn to foreign mfn

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Tue, 17 Apr 2012 10:05:28 +0100
Ian Campbell <Ian.Campbell@citrix.com> wrote:

> On Tue, 2012-04-17 at 02:53 +0100, Mukesh Rathor wrote:
> > On Mon, 16 Apr 2012 14:53:22 +0100
> > Ian Campbell <Ian.Campbell@citrix.com> wrote:
> 
> Sorry, I meant why a whole new subcall instead of a new
> XENMAPSPACE ;-)
> 
> e.g. On ARM I did:
> 
> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> index 86d02c8..b2adfbe 100644
> --- a/xen/include/public/memory.h
> +++ b/xen/include/public/memory.h
> @@ -212,11 +212,13 @@ struct xen_add_to_physmap {
>      uint16_t    size;
>  
>      /* Source mapping space. */
> -#define XENMAPSPACE_shared_info 0 /* shared info page */
> -#define XENMAPSPACE_grant_table 1 /* grant table page */
> -#define XENMAPSPACE_gmfn        2 /* GMFN */
> -#define XENMAPSPACE_gmfn_range  3 /* GMFN range */
> -    unsigned int space;
> +#define XENMAPSPACE_shared_info  0 /* shared info page */
> +#define XENMAPSPACE_grant_table  1 /* grant table page */
> +#define XENMAPSPACE_gmfn         2 /* GMFN */
> +#define XENMAPSPACE_gmfn_range   3 /* GMFN range */
> +#define XENMAPSPACE_gmfn_foreign 4 /* GMFN from another guest */
> +    uint16_t space;
> +    domid_t foreign_domid; /* IFF gmfn_foreign */


Well, for several reasons, I didn't use it, mainly, it doesn't allow
for count. So requests have to come in one frame at a time. Second,
none of the common code can be used by my new request, because:
   - frame is not removed from foreign domain in my case
   - i don't want to update the m2p with new info.

Anyways, I put it there for now. With ballooning change in dom0, I'm
now doing the hcall one frame at a time anyways. We can always enhance
in the future.

        case XENMAPSPACE_gmfn_foreign:
        {
            rc = _add_foreign_to_pmap_batch(&xatp);
            rcu_unlock_domain(d);
            return rc;
        }


>> static long noinline _rem_foreign_pmap_batch(XEN_GUEST_HANDLE(void)
>> arg)  

>Can't XENMEM_remove_from_physmap be used here?

Well, that calls guest_physmap_remove_page() which calls
p2m_remove_page which updates the M2P with INVALID_M2P_ENTRY. Whereas,
i just need to remove from the dom0 p2m and leave M2P as is (mfn to
domU gmfn). I could add a flag to the struct causing it to just call
set_p2m_entry() directly?

thanks,
Mukesh