Re: [Xen-devel] [PATCH 04/18] xen: Preserve reserved grant entries when switching versions

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.01.12 at 18:21, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -2106,6 +2106,7 @@ 
> gnttab_set_version(XEN_GUEST_HANDLE(gnttab_set_version_t uop))
>      struct domain *d = current->domain;
>      struct grant_table *gt = d->grant_table;
>      struct active_grant_entry *act;
> +    grant_entry_v1_t reserved_entries[GNTTAB_NR_RESERVED_ENTRIES];

How much stack space does this consume? (Or in other words, where
does GNTTAB_NR_RESERVED_ENTRIES get defined? It's not in this
patch, I can't find it in earlier patches, and it also doesn't exist in the
current staging tree.)

Jan

>      long res;
>      int i;
>  
> @@ -2126,7 +2127,7 @@ 
> gnttab_set_version(XEN_GUEST_HANDLE(gnttab_set_version_t uop))
>      /* (You need to change the version number for e.g. kexec.) */
>      if ( gt->gt_version != 0 )
>      {
> -        for ( i = 0; i < nr_grant_entries(gt); i++ )
> +        for ( i = GNTTAB_NR_RESERVED_ENTRIES; i < nr_grant_entries(gt); i++ 
> )
>          {
>              act = &active_entry(gt, i);
>              if ( act->pin != 0 )
> @@ -2151,15 +2152,38 @@ 
> gnttab_set_version(XEN_GUEST_HANDLE(gnttab_set_version_t uop))
>              goto out_unlock;
>      }
>  
> +    /* Preserve the first 8 entries (toolstack reserved grants) */
> +    if (gt->gt_version == 1) {
> +        memcpy(reserved_entries, gt->shared_v1[0], sizeof(reserved_entries));
> +    } else if (gt->gt_version == 2) {
> +        for ( i = 0; i < GNTTAB_NR_RESERVED_ENTRIES && i < 
> nr_grant_entries(gt); i++ )
> +        {
> +            reserved_entries[i].flags = shared_entry_v2(gt, i).hdr.flags;
> +            reserved_entries[i].domid = shared_entry_v2(gt, i).hdr.domid;
> +            reserved_entries[i].frame = shared_entry_v2(gt, 
> i).full_page.frame;
> +            reserved_entries[i].flags |= status_entry(gt, i);
> +        }
> +    }
> +
>      if ( op.version < 2 && gt->gt_version == 2 )
>          gnttab_unpopulate_status_frames(d, gt);
>  
> -    if ( op.version != gt->gt_version )
> -    {
> -        /* Make sure there's no crud left over in the table from the
> -           old version. */
> -        for ( i = 0; i < nr_grant_frames(gt); i++ )
> -            memset(gt->shared_raw[i], 0, PAGE_SIZE);
> +    /* Make sure there's no crud left over in the table from the
> +       old version. */
> +    for ( i = 0; i < nr_grant_frames(gt); i++ )
> +        memset(gt->shared_raw[i], 0, PAGE_SIZE);
> +
> +    /* Restore the first 8 entries (toolstack reserved grants) */
> +    if (gt->gt_version != 0 && op.version == 1) {
> +        memcpy(gt->shared_v1[0], reserved_entries, sizeof(reserved_entries));
> +    } else if (gt->gt_version != 0 && op.version == 2) {
> +        for ( i = 0; i < GNTTAB_NR_RESERVED_ENTRIES; i++ )
> +        {
> +            status_entry(gt, i) = reserved_entries[i].flags & 
> (GTF_reading|GTF_writing);
> +            shared_entry_v2(gt, i).hdr.flags = reserved_entries[i].flags & 
> ~(GTF_reading|GTF_writing);
> +            shared_entry_v2(gt, i).hdr.domid = reserved_entries[i].domid;
> +            shared_entry_v2(gt, i).full_page.frame = 
> reserved_entries[i].frame;
> +        }
>      }
>  
>      gt->gt_version = op.version;
> -- 
> 1.7.7.5
> 
> 
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