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

[Hongkaixing <hongkaixing@huawei.com>]

    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.

> -----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);
> 
> 
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