Re: [PATCH] libxc: introduce a per architecture scratch pfn for temporary grant mapping

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2015-01-13 at 20:10 +0000, Julien Grall wrote:

> +int
> +xc_core_arch_get_scratch_gpfn(xc_interface *xch, domid_t domid,
> +                              xen_pfn_t *gpfn)
> +{
> +    /*
> +     * The Grant Table region space is not used until the guest is
> +     * booting. Use the first page for the scrach pfn.

"scratch".

> +     */
> +    XC_BUILD_BUG_ON(GUEST_GNTTAB_SIZE < XC_PAGE_SIZE);
> +
> +    *gpfn = GUEST_GNTTAB_BASE >> XC_PAGE_SHIFT;
> +
> +    return 0;
> +}
> +
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/tools/libxc/xc_core_x86.c b/tools/libxc/xc_core_x86.c
> index f05060a..b157d85 100644
> --- a/tools/libxc/xc_core_x86.c
> +++ b/tools/libxc/xc_core_x86.c
> @@ -205,6 +205,23 @@ xc_core_arch_map_p2m_writable(xc_interface *xch, unsigned int guest_width, xc_do
>      return xc_core_arch_map_p2m_rw(xch, dinfo, info,
>                                     live_shinfo, live_p2m, pfnp, 1);
>  }
> +
> +int
> +xc_core_arch_get_scratch_gpfn(xc_interface *xch, domid_t domid,
> +                              xen_pfn_t *gpfn)
> +{
> +    int rc;
> +
> +    rc = xc_domain_maximum_gpfn(xch, domid);
> +
> +    if ( rc <= 0 )
> +        return rc;
> +
> +    *gpfn = rc;

Shouldn't this be rc + 1 to match the old behaviour?

> +
> +    return 0;
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/tools/libxc/xc_dom_boot.c b/tools/libxc/xc_dom_boot.c
> index f0a1c64..a141eb5 100644
> --- a/tools/libxc/xc_dom_boot.c
> +++ b/tools/libxc/xc_dom_boot.c
> @@ -33,6 +33,7 @@
>  
>  #include "xg_private.h"
>  #include "xc_dom.h"
> +#include "xc_core.h"
>  #include <xen/hvm/params.h>
>  #include <xen/grant_table.h>
>  
> @@ -365,7 +366,7 @@ int xc_dom_gnttab_hvm_seed(xc_interface *xch, domid_t domid,
>                             domid_t xenstore_domid)
>  {
>      int rc;
> -    xen_pfn_t max_gfn;
> +    xen_pfn_t scratch_gpfn;
>      struct xen_add_to_physmap xatp = {
>          .domid = domid,
>          .space = XENMAPSPACE_grant_table,
> @@ -375,16 +376,21 @@ int xc_dom_gnttab_hvm_seed(xc_interface *xch, domid_t domid,
>          .domid = domid,
>      };
>  
> -    max_gfn = xc_domain_maximum_gpfn(xch, domid);
> -    if ( max_gfn <= 0 ) {
> +    rc = xc_core_arch_get_scratch_gpfn(xch, domid, &scratch_gpfn);
> +    if ( rc < 0 )
> +    {
>          xc_dom_panic(xch, XC_INTERNAL_ERROR,
> -                     "%s: failed to get max gfn "
> +                     "%s: failed to get a scratch gfn "
>                       "[errno=%d]\n",
>                       __FUNCTION__, errno);
>          return -1;
>      }
> -    xatp.gpfn = max_gfn + 1;
> -    xrfp.gpfn = max_gfn + 1;
> +    xatp.gpfn = scratch_gpfn;
> +    xrfp.gpfn = scratch_gpfn;
> +
> +    xc_dom_printf(xch, "%s: called, pfn=0x%"PRI_xen_pfn, __FUNCTION__,
> +                  scratch_gpfn);
> +
>  
>      rc = do_memory_op(xch, XENMEM_add_to_physmap, &xatp, sizeof(xatp));
>      if ( rc != 0 )