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

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.


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