Re: [Xen-devel] [PATCH 1/3] x86/xen: allow for privcmd hypercalls to be preempted

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-02-12 at 10:10 +0000, Andrew Cooper wrote:
> On 12/02/14 09:38, Ian Campbell wrote:
> > On Tue, 2014-02-11 at 19:19 +0000, David Vrabel wrote:
> >> Implement is_premptible_hypercall() by adding a second hypercall page
> >> (preemptible_hypercall_page, copied from hypercall_page).  Calls made
> >> via the new page may be preempted.
> > Wouldn't a per-cpu flag variable set for the duration of privcmd_call do
> > the job just as well without requiring per-arch knowledge?
> >
> > Ian.
> >
> 
> Why should privcmd_call be the only preemptible calls?  This code allows
> anyone to voluntarily use the preemptible_hypercall_page.  I would not
> be surprised if modules like gntdev could do with some preemption, but
> it is the long-running toolstack hypercalls which are currently killing
> any loaded XenServer system.

Other sites could equally well use the flag, you could even wrap it up
in xen_preemptible_hypercall_{start,end}.

Ian.


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