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Date: Thu, 7 Dec 2017 17:48:32 +0100
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] in a device or CPU instance init/realize,
 can I rely on something having the BQL or equivalent?
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>

On Thu, 7 Dec 2017 16:05:50 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> Hi; I'm currently writing '-cpu max' support for ARM. For that I'd
> like to be able to do the "probe host kernel for its supported feature
> set" in the CPU object's instance-init function, but I'd like to do
> it just once and cache the answer. Can I rely on something or other
> having the BQL or otherwise ensuring that two threads don't run
> the instance_init method in parallel (eg in a hotplug situation),
> or do I need to create and use my own mutex to protect the cached
> answer data?
considering cached data shouldn't change during qemu lifetime it
shouldn't be possible for instance_init() to clash at hotplug
time as object_new(cpu) calls serialized within monitor/qmp loop.

But why cpu's instance_init, we could cache host's value at
configure_accelerator() time (could be different depending on accel).

CCing Eduardo as he is the one who worked on -cpu max for x86
(If I recall correctly)


> 
> thanks
> -- PMM
>