linux-kernel - Re: [PATCH v5 23/23] KVM: arm64: GICv4.1: Expose HW-based SGIs in debugfs

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Date:   Fri, 20 Mar 2020 20:09:11 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     Auger Eric <eric.auger@...hat.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jason Cooper <jason@...edaemon.net>,
        "Robert Richter" <rrichter@...vell.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "James Morse" <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH v5 23/23] KVM: arm64: GICv4.1: Expose HW-based SGIs in
 debugfs

Hi Marc,

On 2020/3/20 19:46, Marc Zyngier wrote:
>>> Side note: it'd be good to know what the rules are for your own GICv4
>>> implementations, so that we can at least make sure the current code 
>>> is safe.
>>
>> As far as I know, there will be some clean and invalidate operations
>> when v4.0 VPENDBASER.Valid gets programmed.
> 
> Interesting. The ideal behaviour would be that the VPT is up-to-date and
> the caches clean when Valid is cleared (and once Dirty flips to 0).
> 
>> But not sure about behaviors
>> on VMAPP (unmap), it may be a totally v4.1 stuff. I'll have a talk with
>> our SOC team.
> 
> The VMAPP stuff is purely v4.1.
> 
>> But how can the current code be unsafe? Is anywhere in the current code
>> will peek/poke the vpt (whilst GIC continues writing things into it)?
> 
> No. But on VM termination, the memory will be freed, and will eventually be
> reallocated. If the GIC can still write to that memory after it has been
> freed, you end-up with memory corruption... Which is why I'm curious of
> what ensures that on your implementation.

Ah, I got it. I will check it with HiSilicon people next week and go
back to you if the code becomes unsafe due to the incomplete GICv4.


Thanks,
Zenghui