[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: [Xen-devel] pointers in hcalls
> > Message: 1 > Date: Tue, 07 Feb 2006 13:58:05 +1100 > From: Hollis Blanchard <hollisb@xxxxxxxxxx> > Subject: [Xen-devel] pointers in hcalls > To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> > Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx> > Message-ID: <1139281085.13776.29.camel@xxxxxxxxxxxxxxxxxxxxx> > Content-Type: text/plain > > This is a followup to our conversation at the Xen summit about userspace > passing virtual addresses to the hypervisor. > > We talked about an API where data structures would be allocated from a > special area of memory. This API became rather hairy, which we can talk > about. However, it seems to me that the simplest way to handle this is > to disallow pointers entirely, instead embedding the structures in the > higher-level structure. I've had a look through this, and I actually > don't think that would be too bad. > > When performing this conversion, we could initially exempt the > arch-specific hcalls. For consistency I think we'd want to do them all, > but that's not necessary for correctness. Also, constraining these > expanded structures to a single page would be best. > > So I had a look through most (all?) of the hcalls in > xen/include/public/*.h to see which would pose problems. I don't see any > show-stoppers: > - some hcalls, such as dom0_setvcpucontext and dom0_getvcpucontext, > would be trivial to convert. > - I haven't looked at the ACM hcalls in detail, but I think they would > be trivial as well. The acm hypercalls uses pointers when setting and reading the policy from the hypervisor and for dumping statistics. A policy might not necessarily be less than one page. I don't remember the conversation on the Xen summit and probably wasn't involved. Would you mind summarizing briefly the discussion? > - xc_readconsolering() would need to copy up to a page of data into the > caller's buffer. > - it would introduce a hard restriction on the size of the extent array > in the memory operations (though it's worth noting that the balloon > driver already limits this to PAGE_SIZE). > - dom0_perfccontrol and dom0_getdomaininfolist would gain restrictions > similar to the memory ops. > > Thoughts? > > -- > Hollis Blanchard > IBM Linux Technology Thanks Reiner _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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