Re: [Xen-devel] [PATCH V11 4/5] p2m: Always use hostp2m when clipping rangesets

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.12.18 at 10:18, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1002,30 +1002,43 @@ int p2m_change_type_one(struct domain *d, unsigned 
> long gfn_l,
>      return rc;
>  }
>  
> -/* Modify the p2m type of a range of gfns from ot to nt. */
> +/* Modify the p2m type of [start, end) from ot to nt. */
>  static void change_type_range(struct p2m_domain *p2m,
>                                unsigned long start, unsigned long end,
>                                p2m_type_t ot, p2m_type_t nt)
>  {
> -    unsigned long gfn = start;
>      struct domain *d = p2m->domain;
> +    const unsigned long host_max_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
>      int rc = 0;
>  
> -    if ( unlikely(end > p2m->max_mapped_pfn) )
> -    {
> -        if ( !gfn )
> -        {
> -            p2m->change_entry_type_global(p2m, ot, nt);
> -            gfn = end;
> -        }
> -        end = p2m->max_mapped_pfn + 1;
> -    }
> -    if ( gfn < end )
> -        rc = p2m->change_entry_type_range(p2m, ot, nt, gfn, end - 1);
> +    --end;
> +
> +    if ( start >= host_max_pfn )
> +        printk(XENLOG_G_WARNING "Dom%d logdirty rangeset clipped to 
> max_mapped_pfn\n",
> +               d->domain_id);
> +
> +    /* Always clip the rangeset down to the host p2m. */
> +    if ( unlikely(end > host_max_pfn) )
> +        end = host_max_pfn;
> +
> +    /* If the requested range is out of scope, return doing nothing. */
> +    if ( start > end )
> +        return;

My prior comment remains: Even if there's no change in behavior
(and you avoid the assertion), especially due to the comment the
impression results (at least to me) that all is well here, when it
really is a (latent) bug to "do nothing" in this case. George, so far
this was a discussion between Razvan and me - do you have an
opinion either way here?

Jan



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