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

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Date:   Fri, 22 Jan 2021 11:47:51 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Yanan Wang <wangyanan55@...wei.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Gavin Shan <gshan@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        wanghaibin.wang@...wei.com, yezengruan@...wei.com,
        yuzenghui@...wei.com
Subject: Re: [RFC PATCH v4 0/2] Some optimization for stage-2 translation

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...