Re: [RFC PATCH v4 0/2] Some optimization for stage-2 translation

From: Marc Zyngier <maz@kernel.org>
To: Yanan Wang <wangyanan55@huawei.com>
Cc: Gavin Shan <gshan@redhat.com>,
	kvm@vger.kernel.org, Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Quentin Perret <qperret@google.com>,
	linux-kernel@vger.kernel.org, yezengruan@huawei.com,
	James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	yuzenghui@huawei.com, wanghaibin.wang@huawei.com,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH v4 0/2] Some optimization for stage-2 translation
Date: Fri, 22 Jan 2021 11:47:51 +0000	[thread overview]
Message-ID: <a6d4d16574fa76c4e519cdbff70cf950@kernel.org> (raw)
In-Reply-To: <20210122101358.379956-1-wangyanan55@huawei.com>

Hi Yanan,

On 2021-01-22 10:13, Yanan Wang wrote:
> Hi, Will, Marc,
> Is there any further comment on the v3 series I post previously?

None, I was planning to queue them for 5.12 over the weekend.

> If they are not fine to you, then I think maybe we should just turn
> back to the original solution in v1, where I suggestted to filter out
> the case of only updating access permissions in the map handler and
> handle it right there.
> 
> Here are the reasons for my current opinion:
> With an errno returned from the map handler for this single case, there
> will be one more vcpu exit from guest and we also have to consider the
> spurious dirty pages. Besides, it seems that the EAGAIN errno has been
> chosen specially for this case and can not be used elsewhere for other
> reasons, as we will change this errno to zero at the end of the 
> function.
> 
> The v1 solution looks like more concise at last, so I refine the diff
> and post the v4 with two patches here, just for a contrast.
> 
> Which solution will you prefer now? Could you please let me know.

I'm still very much opposed to mixing mapping and permission changes.
How bad is the spurious return to a vcpu?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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