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SubjectRe: [PATCH 2/3] perf: require exclude_guest to use PEBS - kernel side enforcement
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Hi David,

On Wed, 12 Sep 2012 09:16:29 -0600, David Ahern wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> Per Peter:
> "Intel PEBS in VT-x context uses the DS address as a guest linear address,
> even though its programmed by the host as a host linear address. This
> either results in guest memory corruption and or the hardware faulting and
> 'crashing' the virtual machine. Therefore we have to disable PEBS on VT-x
> enter and re-enable on VT-x exit, enforcing a strict exclude_guest.
>
> This patch enforces exclude_guest kernel side.
>
[snip]
> @@ -380,6 +383,9 @@ int x86_pmu_hw_config(struct perf_event *event)
> if (event->attr.precise_ip) {
> int precise = 0;
>
> + if (!event->attr.exclude_guest)
> + return -EOPNOTSUPP;

I see a whitespace problem here. :)

Thanks,
Namhyung


> +
> /* Support for constant skid */
> if (x86_pmu.pebs_active && !x86_pmu.pebs_broken) {
> precise++;


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