Re: [Xen-devel] [PATCH 3/3] x86: tighten MMU_*PT_UPDATE* check and combine error paths

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/10/17 11:01, Jan Beulich wrote:
> Don't accept anything other than r/w RAM pages and move the paged-out
> check into the (unlikely) error path following that check.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

How does dom0 boot with this change in place?  You appear to have
prohibited mapping MMIO frames.

~Andrew

>
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -3507,18 +3507,18 @@ long do_mmu_update(
>              gmfn = req.ptr >> PAGE_SHIFT;
>              page = get_page_from_gfn(pt_owner, gmfn, &p2mt, P2M_ALLOC);
>  
> -            if ( p2m_is_paged(p2mt) )
> +            if ( unlikely(!page) || p2mt != p2m_ram_rw )
>              {
> -                ASSERT(!page);
> -                p2m_mem_paging_populate(pt_owner, gmfn);
> -                rc = -ENOENT;
> -                break;
> -            }
> -
> -            if ( unlikely(!page) )
> -            {
> -                gdprintk(XENLOG_WARNING,
> -                         "Could not get page for normal update\n");
> +                if ( page )
> +                    put_page(page);
> +                if ( p2m_is_paged(p2mt) )
> +                {
> +                    p2m_mem_paging_populate(pt_owner, gmfn);
> +                    rc = -ENOENT;
> +                }
> +                else
> +                    gdprintk(XENLOG_WARNING,
> +                             "Could not get page for normal update\n");
>                  break;
>              }
>  
>
>
>


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