Re: [Xen-devel] [PATCH v10 5/6] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.04.17 at 20:04, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -288,6 +288,10 @@ int guest_remove_page(struct domain *d, unsigned long 
> gmfn)
>           put_gfn(d, gmfn);
>           return 1;
>       }
> +    if ( unlikely(p2mt == p2m_ioreq_server) )
> +        p2m_change_type_one(d, gmfn,
> +                            p2m_ioreq_server, p2m_ram_rw);
> +
>   #else
>       mfn = gfn_to_mfn(d, _gfn(gmfn));
>   #endif

To be honest, this looks more like a quick hack than a proper solution
at the first glance. To me it would seem preferable if the count was
adjusted at the point the P2M entry is being replaced (i.e. down the
call stack from guest_physmap_remove_page()). The closer to the
actual changing of the P2M entry, the less likely you miss any call
paths (as was already explained by George while suggesting to put
the accounting into the leaf most EPT/NPT functions).

Jan


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