RE: [Xen-devel] guest physical to xen machine copy?

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Hmmm...  gfn_to_mfn() when used as below seems to just
return the original gfn, e.g.

guest_mfn = gfn_to_mfn(current->domain,gpfn,&t);

Is this correct?  Note that current->domain is a 32-bit
paravirtualized domain and xen is 64-bit, if that matters.
(Is there a better way if one knows that the domain is
always pv?)

> Use p2m_is_ram() instead of checking individual p2m ram type

In copying the other direction (e.g. copy_page_TO_guest),
I think I need to check for t==p2m_ram_rw, right?
If so, the "Not necessarily true" comment in static
inline _gfn_to_mfn in include/asm-x86/p2m.h worries me.
Should it?

Dan

> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> Sent: Monday, September 29, 2008 12:49 AM
> To: Dan Magenheimer; Xen-Devel (E-mail); Tian, Kevin
> Subject: Re: [Xen-devel] guest physical to xen machine copy?
>
>
> On 28/9/08 21:19, "Dan Magenheimer"
> <dan.magenheimer@xxxxxxxxxx> wrote:
>
> >> You can try gfn_to_mfn.
> >
> > Thanks!  Then if I have a page_info pointer and a gpfn, will
> > this code work for copying?  Or can it be made simpler?
>
> Use p2m_is_ram() instead of checking individual p2m ram type
> enumerations.
> Use [un]map_domain_page instead of [un]map_domain_page_global.
>
>  -- Keir
>
> > Thanks,
> > Dan
> >
> > #include <asm/p2m.h>
> > static int
> > copy_page_from_guest(struct page_info *dst_pi,
> XEN_GUEST_HANDLE(void) gpfn)
> > {
> >     int i;
> >     unsigned long dst_mfn, guest_mfn;
> >     void *dst_va, *guest_va;
> >     p2m_type_t t;
> >
> >     if (is_pv_32on64_vcpu(current))
> >         gpfn.p = (void *)((unsigned long)gpfn.p & 0xfffffUL);
> >     dst_mfn = page_to_mfn(dst_pi);
> >     guest_mfn = gfn_to_mfn(current->domain,(unsigned
> long)gpfn.p,&t);
> >     if (t != p2m_ram_rw && t != p2m_ram_ro)
> >         return(0);  /* do I need to worry about p2m_ram_logdirty? */
> >     dst_va = map_domain_page_global(dst_mfn);
> >     guest_va = map_domain_page_global(guest_mfn);
> > /*  i = __copy_from_guest(dst_va, guest_va, PAGE_SIZE); */
> >     i = __copy_from_user(dst_va, guest_va, PAGE_SIZE);
> >     unmap_domain_page_global(guest_va);
> >     unmap_domain_page_global(dst_va);
> >     return (!i);
> > }
> >
> >
> >> -----Original Message-----
> >> From:
> >> Sent: Saturday, September 27, 2008 8:38 PM
> >> To: Dan Magenheimer; Xen-Devel (E-mail)
> >> Subject: RE: [Xen-devel] guest physical to xen machine copy?
> >>
> >>
> >> You can try gfn_to_mfn...
> >>
> >> Thanks,
> >> Kevin
> >>
> >>> From: Dan Magenheimer
> >>> Sent: 2008年9月28日 5:33
> >>>
> >>> Sorry for my poor x86 memory model knowlege...
> >>>
> >>> In some code I am working on, I currently pass the
> >>> address of a guest page from a domain via a hypercall
> >>> and in Xen either copy to or from the guest page
> >>> using:
> >>>
> >>> __copy_from_guest(xen_va, guest_va, PAGE_SIZE)
> >>>
> >>> or
> >>>
> >>> __copy_to_guest(guest_va, xen_va, PAGE_SIZE)
> >>>
> >>> where guest_va is declared as a XEN_GUEST_HANDLE(void)
> >>>
> >>> Now I'd like to switch the hypercall interface so
> >>> that the domain passes a guest physical address
> >>> (or guest physical frame number) instead of a guest
> >>> virtual address.
> >>>
> >>> I see code that does get_gpfn_from_mfn() but not
> >>> the opposite.  What do I need to do to copy a
> >>> page of data from a guest pfn to a Xen mfn (or
> >>> vice versa)?  And is a guest physical address
> >>> still referenced as a XEN_GUEST_HANDLE?
> >>>
> >>> It's probably very simple but I can't find it...
> >>>
> >>> Thanks,
> >>> Dan
> >>>
> >>> P.S. This has to work on 32- or 64-bit guests to
> >>> both 32- and 64-bit hypervisors.
> >>>
> >>> _______________________________________________
> >>> Xen-devel mailing list
> >>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >>> http://lists.xensource.com/xen-devel
> >>>
> >>
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
>
>
>

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