Re: [Xen-devel] [PATCH 03 of 12] x86/mm: Add per-page locking for memory sharing, when audits are disabled

[Tim Deegan <tim@xxxxxxx>]

At 05:06 -0800 on 19 Jan (1326949574), Andres Lagar-Cavilla wrote:
> > At 21:56 -0500 on 15 Jan (1326664583), Andres Lagar-Cavilla wrote:
> >> @@ -510,26 +684,63 @@ int mem_sharing_share_pages(struct domai
> >>      smfn = get_gfn(sd, sgfn, &smfn_type);
> >>      cmfn = get_gfn(cd, cgfn, &cmfn_type);
> >>
> >> -    ret = XEN_DOMCTL_MEM_SHARING_S_HANDLE_INVALID;
> >> -    spage = mem_sharing_lookup(mfn_x(smfn));
> >> -    if ( spage == NULL )
> >> +    /* This tricky business is to avoid two callers deadlocking if
> >> +     * grabbing pages in opposite client/source order */
> >
> > I think you need to delete the XXX comment just above. :)
> >
> Well, that XXX comment applies if get_gfn locks the p2m, and then what
> we're grabbing in mem_sharing_lookup are lock per mfn, essentially. To

Oh, I see - wrong deadlock!. :)

Tim.

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