[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [patch 18/21] Xen-paravirt: Add Xen grant table support
Andrew Morton wrote: > On Thu, 15 Feb 2007 18:25:07 -0800 Jeremy Fitzhardinge <jeremy@xxxxxxxx> > wrote: > > >> +int gnttab_grant_foreign_access(domid_t domid, unsigned long frame, >> + int readonly) >> +{ >> + int ref; >> + >> + if (unlikely((ref = get_free_entry()) == -1)) >> + return -ENOSPC; >> + >> + shared[ref].frame = frame; >> + shared[ref].domid = domid; >> + wmb(); >> + shared[ref].flags = GTF_permit_access | (readonly ? GTF_readonly : 0); >> + >> + return ref; >> +} >> +EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access); >> > > We have lots of open-coded mysteriously unexplained barriers in here. > > I assume they're not smp_wmb() because this could be a !SMP guest talking > to an SMP host? > Yeah. The grant tables refer to pages which are shared with other domains, so they could be running on other cpus even if this domain is UP. There's a lockless protocol going on here, but I'll need to look it up and sprinkle some comments. J _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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