[Xen-devel] Re: [PATCH] EPT: Flush running cpus, add mask to flush when scheduled in

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

Oops, patch...
 -George

On Mon, Sep 21, 2009 at 7:04 PM, George Dunlap
<George.Dunlap@xxxxxxxxxxxxx> wrote:
> The attached patch modifies ept_sync_domain() to make it more
> efficient wrt flushing ept translations.
>
> Specifically:
> * It synchronously flushes only cpus on which the domain is currently
> running (d->domain_dirty_cpumask)
> * It introduces a new vmx-specific mask, "ept_needs_flush", set to the
> complement of d->domain_dirty_cpumask
> * In vmx_ctxt_switch_to(), if the cpu is set in ept_needs_flush, it
> flushes ept before running.
>
> Main change I'd like reviewed: in order to avoid a potential race
> condition described below, I had to re-order the setting of
> domain_dirty_cpumask and the calling of arch.ctxt_switch_to() in
> __context_switch().
>
> Potential race without the re-ordering:
> p1: change ept
> p2: check ept_needs_flush, finds it false, doesn't flush
> p1: sets ept_needs_flush
> p1: checks domain_dirty, finds p2 not in it
> p2: sets domain_dirty
>
> Thus the vcpu on p2 is scheduled without its ept translations being flushed.
>
> I've tested this with a 2-vcpu VM doing a parallel compile and
> ballooning, no problems.
>
> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>

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