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From: Peter Maydell <peter.maydell@linaro.org>
Date: Fri, 29 Jul 2016 16:29:03 +0100
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Subject: Re: [Qemu-devel] [PATCH RFC 1/1] arm64: add an option to turn
 on/off vpmu support
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To: Andrew Jones <drjones@redhat.com>
Cc: Wei Huang <wei@redhat.com>, qemu-arm <qemu-arm@nongnu.org>, QEMU Developers <qemu-devel@nongnu.org>, Shannon Zhao <shannon.zhao@linaro.org>, Andrea Bolognani <abologna@redhat.com>

On 29 July 2016 at 07:54, Andrew Jones <drjones@redhat.com> wrote:
> OK, so this property will be exposed to all ARM cpu types, and if a user
> turns it on, then it will stay on for all types, except when using KVM
> with an aarch64 cpu type, and KVM doesn't support it. This could mislead
> users to believe they'll get a pmu, by simply adding pmu=on, even when
> they can't. I think we'd ideally keep has_pmu, and the current code that
> sets it, and then add code like
>
>  if (enable_pmu && !has_pmu) {
>    error_report("Warning: ...")
>  }
>
> somewhere.

I think we should probably follow the existing model used by
has_el3, where the property only exists if it's valid to set it.

thanks
-- PMM