Re: [PATCH RFC v13 19/20] PVH xen tools: libxc changes to build a PVH guest.

[George Dunlap <george.dunlap@eu.citrix.com>]

On 18/10/13 17:45, Roger Pau Monné wrote:
> This patch is incomplete, PVH guests with 4GB of RAM or more will fail
> to boot due to libxc temporary mapping the grant table to gfn 0xFFFFE,
> which is an invalid gfn on HVM guests, but not on PVH guests. When
> libxc removes the mapping of 0xFFFFE it will leave an invalid mfn in
> the p2m table, that will make the guest crash when trying to access
> that gfn.
>
> The easiest way I've found to solve this is to temporary map the grant
> table to the maximum gfn + 1. This fixes the PVH issue, and also seems
> to work fine with HVM guests, here is the diff which should probably be
> integrated into this patch:

Thanks Roger.  I assume it's OK to add your sign-off to this patch?

  -George

>
> ---
> diff --git a/tools/libxc/xc_dom.h b/tools/libxc/xc_dom.h
> index 5168bcd..90679da 100644
> --- a/tools/libxc/xc_dom.h
> +++ b/tools/libxc/xc_dom.h
> @@ -18,9 +18,6 @@
>   
>   #define INVALID_P2M_ENTRY   ((xen_pfn_t)-1)
>   
> -/* Scrach PFN for temporary mappings in HVM */
> -#define SCRATCH_PFN_GNTTAB 0xFFFFE
> -
>   /* --- typedefs and structs ---------------------------------------- */
>   
>   typedef uint64_t xen_vaddr_t;
> diff --git a/tools/libxc/xc_dom_boot.c b/tools/libxc/xc_dom_boot.c
> index 71e1897..fdfeaf8 100644
> --- a/tools/libxc/xc_dom_boot.c
> +++ b/tools/libxc/xc_dom_boot.c
> @@ -361,17 +361,27 @@ int xc_dom_gnttab_hvm_seed(xc_interface *xch, domid_t domid,
>                              domid_t xenstore_domid)
>   {
>       int rc;
> +    xen_pfn_t max_gfn;
>       struct xen_add_to_physmap xatp = {
>           .domid = domid,
>           .space = XENMAPSPACE_grant_table,
>           .idx   = 0,
> -        .gpfn  = SCRATCH_PFN_GNTTAB
>       };
>       struct xen_remove_from_physmap xrfp = {
>           .domid = domid,
> -        .gpfn  = SCRATCH_PFN_GNTTAB
>       };
>   
> +    max_gfn = xc_domain_maximum_gpfn(xch, domid);
> +    if ( max_gfn <= 0 ) {
> +        xc_dom_panic(xch, XC_INTERNAL_ERROR,
> +                     "%s: failed to get max gfn "
> +                     "[errno=%d]\n",
> +                     __FUNCTION__, errno);
> +        return -1;
> +    }
> +    xatp.gpfn = max_gfn + 1;
> +    xrfp.gpfn = max_gfn + 1;
> +
>       rc = do_memory_op(xch, XENMEM_add_to_physmap, &xatp, sizeof(xatp));
>       if ( rc != 0 )
>       {
>