Re: [PATCH 1 of 2] x86/mm: Allow a page in p2m_ram_paged_out state to be loaded

[Hongkaixing <hongkaixing@huawei.com>]

> -----Original Message-----
> From: Andres Lagar-Cavilla [mailto:andres@lagarcavilla.org]
> Sent: Wednesday, January 11, 2012 10:57 PM
> To: Hongkaixing
> Cc: xen-devel@lists.xensource.com; andres@gridcentric.ca; tim@xen.org; olaf@aepfle.de; adin@gridcentric.ca;
> yanqiangjun@huawei.com; bicky.shi@huawei.com; xiaowei.yang@huawei.com
> Subject: RE: [Xen-devel] [PATCH 1 of 2] x86/mm: Allow a page in p2m_ram_paged_out state to be loaded
> 
> I think top-posting is frowned upon. Below...
> >     I think it may have many unpredicted risks.
> >     After p2mt is changed to p2m_ram_rw, Domain guest can access this page
> > unrestrictedly without being trapped in xen.
> >  But at this time, the page is not prepared.
> 
> Nope. The page has already been allocated and paged-in (copy_from_user out
> of user_ptr) by the time the p2mt is changed


I have got it,  first change p2mt to p2m_ram_paging_in, prepare a page, use copy_from_usr to copy, then change p2mt to ram_rw . It
is a good idea.



> Andres
> >
> >> -----Original Message-----
> >> From: xen-devel-bounces@lists.xensource.com
> >> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Andres
> >> Lagar-Cavilla
> >> Sent: Tuesday, January 10, 2012 5:41 AM
> >> To: xen-devel@lists.xensource.com
> >> Cc: andres@gridcentric.ca; tim@xen.org; olaf@aepfle.de;
> >> adin@gridcentric.ca
> >> Subject: [Xen-devel] [PATCH 1 of 2] x86/mm: Allow a page in
> >> p2m_ram_paged_out state to be loaded
> >>
> >>  xen/arch/x86/mm/p2m.c |  15 +++++++++++----
> >>  1 files changed, 11 insertions(+), 4 deletions(-)
> >>
> >>
> >> This removes the need for a page to be accessed in order to be pageable
> >> again. A pager can now page-in pages at will with no need to map them
> >> in a separate thread.
> >>
> >> Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
> >> Acked-by: Tim Deegan <tim@xen.org>
> >>
> >> diff -r 90f764bf02c3 -r f7c330d5b4b5 xen/arch/x86/mm/p2m.c
> >> --- a/xen/arch/x86/mm/p2m.c
> >> +++ b/xen/arch/x86/mm/p2m.c
> >> @@ -964,7 +964,7 @@ void p2m_mem_paging_populate(struct doma
> >>  int p2m_mem_paging_prep(struct domain *d, unsigned long gfn, uint64_t
> >> buffer)
> >>  {
> >>      struct page_info *page;
> >> -    p2m_type_t p2mt;
> >> +    p2m_type_t p2mt, target_p2mt;
> >>      p2m_access_t a;
> >>      mfn_t mfn;
> >>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
> >> @@ -982,8 +982,8 @@ int p2m_mem_paging_prep(struct domain *d
> >>      mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
> >>
> >>      ret = -ENOENT;
> >> -    /* Allow only missing pages */
> >> -    if ( p2mt != p2m_ram_paging_in_start )
> >> +    /* Allow missing pages */
> >> +    if ( (p2mt != p2m_ram_paging_in_start) && (p2mt != p2m_ram_paged) )
> >>          goto out;
> >>
> >>      /* Allocate a page if the gfn does not have one yet */
> >> @@ -1018,8 +1018,15 @@ int p2m_mem_paging_prep(struct domain *d
> >>          }
> >>      }
> >>
> >> +    target_p2mt = (p2mt == p2m_ram_paging_in_start) ?
> >> +        /* If we kicked the pager with a populate event, the pager will
> >> send
> >> +         * a resume event back */
> >> +        p2m_ram_paging_in :
> >> +        /* If this was called asynchronously by the pager, then we can
> >> +         * transition directly to the final guest-accessible type */
> >> +        (paging_mode_log_dirty(d) ? p2m_ram_logdirty : p2m_ram_rw);
> >>      /* Fix p2m mapping */
> >> -    set_p2m_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2m_ram_paging_in, a);
> >> +    set_p2m_entry(p2m, gfn, mfn, PAGE_ORDER_4K, target_p2mt, a);
> >>
> >>      atomic_dec(&d->paged_pages);
> >>
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@lists.xensource.com
> >> http://lists.xensource.com/xen-devel
> >
> >