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Date: Mon, 18 Sep 2023 10:05:36 -0700
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From: Oliver Upton <oliver.upton@linux.dev>
To: Will Deacon <will@kernel.org>
Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Salil Mehta <salil.mehta@huawei.com>
Subject: Re: [PATCH kvmtool v3 08/17] Add helpers to pause the VM from vCPU
 thread
Message-ID: <ZQiDYLgicCnXA5a0@linux.dev>
References: <20230802234255.466782-1-oliver.upton@linux.dev>
 <20230802234255.466782-9-oliver.upton@linux.dev>
 <20230918104028.GA17744@willie-the-truck>
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In-Reply-To: <20230918104028.GA17744@willie-the-truck>
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Hey Will,

On Mon, Sep 18, 2023 at 11:40:28AM +0100, Will Deacon wrote:
> On Wed, Aug 02, 2023 at 11:42:46PM +0000, Oliver Upton wrote:
> > +void kvm_cpu__pause_vm(struct kvm_cpu *vcpu)
> > +{
> > +	/*
> > +	 * Mark the calling vCPU as paused to avoid waiting indefinitely for a
> > +	 * signal exit.
> > +	 */
> > +	vcpu->paused = true;
> > +	kvm__pause(vcpu->kvm);
> > +}
> > +
> > +void kvm_cpu__continue_vm(struct kvm_cpu *vcpu)
> > +{
> > +	vcpu->paused = false;
> > +	kvm__continue(vcpu->kvm);
> > +}
> 
> Why is it safe to manipulate 'vcpu->paused' here without the pause_lock
> held?

Heh, I hacked this up to get _something_ working and never re-evaluated
the locking that I completely sidestepped.

> Relatedly, how does this interact with the 'pause' and 'resume'
> lkvm commands?

Poorly, if I had to guess. I hadn't actually tested with them. I'll take
another crack at this to safely quiesce when handling calls.

Thanks for having a look.

-- 
Best,
Oliver