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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. > > > > 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). It's just that the check would be wrong if we allow Xen itself to use a different page size than the one used by the grant table interface to the guest. > > > > > Furthermore, it would add a comment explaining where this limit comes from. > > > > > > Lastly, did you check the compiler wouldn't throw an error on arm32? > > > > I've tested a previous version (v2), but not this one. I assume it > > doesn't build? > > I haven't tried. But I remember in the past seen report for always > true/false check. Maybe that was just on coverity? Hm, possibly. It seems like debian-unstable arm32 gcc is building OK, but I've got no idea if different compiler versions could complain. Thanks, Roger.