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Message-ID: <155838f4-eac0-4e8c-adc6-e4efa2a786e2@linux.intel.com>
Date:   Thu, 13 Jul 2023 12:02:09 +0800
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Cc:     baolu.lu@linux.intel.com, "Tian, Kevin" <kevin.tian@intel.com>,
        Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Nicolin Chen <nicolinc@nvidia.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/9] iommu: Add common code to handle IO page faults
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To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
References: <20230711010642.19707-1-baolu.lu@linux.intel.com>
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 <cbbe1175-40f3-805e-02c2-f887b3289f04@linux.intel.com>
 <20230712094522.GB507884@myrica>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20230712094522.GB507884@myrica>
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On 2023/7/12 17:45, Jean-Philippe Brucker wrote:
> On Wed, Jul 12, 2023 at 10:32:13AM +0800, Baolu Lu wrote:
>>> btw is there value of moving the group handling logic from
>>> iommu_queue_iopf() to this common function?
>>>
>>> I wonder whether there is any correctness issue if not forwarding
>>> partial request to iommufd. If not this can also help reduce
>>> notifications to the user until the group is ready.
>>
>> I don't think there's any correctness issue. But it should be better if
>> we can inject the page faults to vm guests as soon as possible. There's
>> no requirement to put page requests to vIOMMU's hardware page request
>> queue at the granularity of a fault group. Thoughts?
> 
> Not sure I understand you correctly, but we can't inject partial fault
> groups: if the HW PRI queue overflows, the last fault in a group may be
> lost, so the non-last faults in that group already injected won't be
> completed (until PRGI reuse), leaking PRI request credits and guest
> resources.

Yeah, that's how vIOMMU injects the faults. On host/hypervisor side, my
understanding is that faults should be uploaded as soon as possible.

Best regards,
baolu