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> > > > > > /* Lock protecting the maptrack limit */ > > > > > > spinlock_t maptrack_lock; > > > > > > + unsigned int max_version; > > > > > > /* > > > > > > * Defaults to v1. May be changed with GNTTABOP_set_version. All other > > > > > > * values are invalid. > > > > > > @@ -1917,11 +1918,33 @@ active_alloc_failed: > > > > > > } > > > > > > int grant_table_init(struct domain *d, int max_grant_frames, > > > > > > - int max_maptrack_frames) > > > > > > + int max_maptrack_frames, unsigned int options) > > > > > > { > > > > > > struct grant_table *gt; > > > > > > + unsigned int max_grant_version = options & XEN_DOMCTL_GRANT_version_mask; > > > > > > int ret = -ENOMEM; > > > > > > + if ( max_grant_version == XEN_DOMCTL_GRANT_version_default ) > > > > > > + max_grant_version = opt_gnttab_max_version; > > > > > > + if ( !max_grant_version ) > > > > > > + { > > > > > > + dprintk(XENLOG_INFO, "%pd: invalid grant table version 0 requested\n", > > > > > > + d); > > > > > > + return -EINVAL; > > > > > > + } > > > > > > + if ( max_grant_version > opt_gnttab_max_version ) > > > > > > + { > > > > > > + dprintk(XENLOG_INFO, > > > > > > + "%pd: requested grant version (%u) greater than supported (%u)\n", > > > > > > + d, max_grant_version, opt_gnttab_max_version); > > > > > > + return -EINVAL; > > > > > > + } > > > > > > + if ( unlikely(max_page >= PFN_DOWN(TB(16))) && is_pv_domain(d) && > > > > > > > > > > From my understanding, the limit for the grant table v1 is based on the page > > > > > granularity used and the size of the fields. > > > > > > > > > > So the limit you add is valid for 4KB but not 16KB/64KB. Therefore, I think > > > > > it would be better to use: > > > > > > > > > > 'max_page >= (1U << 32)' > > > > > > > > I'm slightly confused. Isn't Xen always using a 4KB page granularity, > > > > > > Yes. We only support 4KB today. But most of Xen is agnostic to the page > > > granularity. I have actually started to look to allow 64KB/16KB page > > > granularity for Xen on Arm in my spare time. > > > > > > > and that also applies to the grant table entries? > > > The page granularity for the hypercall interface is whatever the page > > > granularity Xen is using. So... > > > > I've somehow assumed that the current hypercall ABI was strictly tied > > to 4KB pages, as that's for example already hardcoded in Linux > > as XEN_PAGE_SIZE. > > It is a mess. Before, XEN_PAGE_SIZE was introduced, we were assuming that > Linux and Xen were using the same page granularity. > > When I introduced the support to run guest with 16KB and 64KB, then we > decided to introduce the define. Looking back at the decision, this was a > mistake and we should have introduced an hypercall to fetch the ABI > granularity instead. > > > > > > > > > > > I don't think it's possible to use correctly use a 16KB or 64KB page > > > > as an entry for the grant table, as Xen assumes those to always be 4KB > > > > based. > > > > > > ... if you build Xen with 16KB, then the grant table entries will be using > > > 16KB. > > > > > > So I would like to avoid making the assumption that we are always using 4KB. > > > That said, the worse that can happen is a spurious message. So this is more > > > to get an accurate check. > > > > I don't have strong objections to using max_page >> 32, it might even > > be clearer than checking against TB(16). FWIW, I've changed the check to use >> 32 and limited it to CONFIG_64BIT, since on 32bit arches max_page will be a 32bit value. Thanks, Roger.