linux-kernel - Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

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Date:   Mon, 20 Jun 2022 11:11:01 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Nicolin Chen <nicolinc@...dia.com>
Cc:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "jordan@...micpenguin.net" <jordan@...micpenguin.net>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "will@...nel.org" <will@...nel.org>,
        "alyssa@...enzweig.io" <alyssa@...enzweig.io>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "saiprakash.ranjan@...eaurora.org" <saiprakash.ranjan@...eaurora.org>,
        "zhang.lyra@...il.com" <zhang.lyra@...il.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "yangyingliang@...wei.com" <yangyingliang@...wei.com>,
        "orsonzhai@...il.com" <orsonzhai@...il.com>,
        "gerald.schaefer@...ux.ibm.com" <gerald.schaefer@...ux.ibm.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "christophe.jaillet@...adoo.fr" <christophe.jaillet@...adoo.fr>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "isaacm@...eaurora.org" <isaacm@...eaurora.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "marcan@...can.st" <marcan@...can.st>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolin.wang7@...il.com" <baolin.wang7@...il.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

On 2022-06-17 03:53, Tian, Kevin wrote:
>> From: Nicolin Chen <nicolinc@...dia.com>
>> Sent: Friday, June 17, 2022 6:41 AM
>>
>>> ...
>>>> -     if (resv_msi) {
>>>> +     if (resv_msi && !domain->msi_cookie) {
>>>>                ret = iommu_get_msi_cookie(domain->domain,
>>>> resv_msi_base);
>>>>                if (ret && ret != -ENODEV)
>>>>                        goto out_detach;
>>>> +             domain->msi_cookie = true;
>>>>        }
>>>
>>> why not moving to alloc_attach_domain() then no need for the new
>>> domain field? It's required only when a new domain is allocated.
>>
>> When reusing an existing domain that doesn't have an msi_cookie,
>> we can do iommu_get_msi_cookie() if resv_msi is found. So it is
>> not limited to a new domain.
> 
> Looks msi_cookie requirement is per platform (currently only
> for smmu. see arm_smmu_get_resv_regions()). If there is
> no mixed case then above check is not required.
> 
> But let's hear whether Robin has a different thought here.

Yes, the cookie should logically be tied to the lifetime of the domain 
itself. In the relevant context, "an existing domain that doesn't have 
an msi_cookie" should never exist.

Thanks,
Robin.