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b=Ha8SxzK+rGcb3Wm7KpPZTYivnusdu/64e1tjoR+SsWLZTwkJ0vsCZoCO/9EobXlBvdLtfk wUj9vpTjoWI0je8ez8Tql/bQ61ZYkTijKU/EU21APgEg8qAzSgg45Cs3jrx+qXXyb4r+VY EPk7sgfiYPy8ldRHjjTOeRppGX55RCw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-75-hM7QRMx5P1iP3uP3ubMk9g-1; Thu, 16 Apr 2020 08:42:51 -0400 X-MC-Unique: hM7QRMx5P1iP3uP3ubMk9g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6CB611084424; Thu, 16 Apr 2020 12:42:49 +0000 (UTC) Received: from [10.36.115.53] (ovpn-115-53.ams2.redhat.com [10.36.115.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E96485C1C5; Thu, 16 Apr 2020 12:42:39 +0000 (UTC) Subject: Re: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE_INVALIDATE To: "Tian, Kevin" , "Liu, Yi L" , Alex Williamson References: <1584880325-10561-1-git-send-email-yi.l.liu@intel.com> <1584880325-10561-8-git-send-email-yi.l.liu@intel.com> <20200402142428.2901432e@w520.home> <20200403093436.094b1928@w520.home> From: Auger Eric Message-ID: <7d13bdbb-e972-c301-0970-90f63ecf69fc@redhat.com> Date: Thu, 16 Apr 2020 14:42:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Cc: "jean-philippe@linaro.org" , "Raj, Ashok" , "kvm@vger.kernel.org" , "Tian, Jun J" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "Sun, Yi Y" , "Wu, Hao" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi Kevin, On 4/16/20 2:09 PM, Tian, Kevin wrote: >> From: Liu, Yi L >> Sent: Thursday, April 16, 2020 6:40 PM >> >> Hi Alex, >> Still have a direction question with you. Better get agreement with you >> before heading forward. >> >>> From: Alex Williamson >>> Sent: Friday, April 3, 2020 11:35 PM >> [...] >>>>>> + * >>>>>> + * returns: 0 on success, -errno on failure. >>>>>> + */ >>>>>> +struct vfio_iommu_type1_cache_invalidate { >>>>>> + __u32 argsz; >>>>>> + __u32 flags; >>>>>> + struct iommu_cache_invalidate_info cache_info; >>>>>> +}; >>>>>> +#define VFIO_IOMMU_CACHE_INVALIDATE _IO(VFIO_TYPE, >>> VFIO_BASE >>>>> + 24) >>>>> >>>>> The future extension capabilities of this ioctl worry me, I wonder if >>>>> we should do another data[] with flag defining that data as >> CACHE_INFO. >>>> >>>> Can you elaborate? Does it mean with this way we don't rely on iommu >>>> driver to provide version_to_size conversion and instead we just pass >>>> data[] to iommu driver for further audit? >>> >>> No, my concern is that this ioctl has a single function, strictly tied >>> to the iommu uapi. If we replace cache_info with data[] then we can >>> define a flag to specify that data[] is struct >>> iommu_cache_invalidate_info, and if we need to, a different flag to >>> identify data[] as something else. For example if we get stuck >>> expanding cache_info to meet new demands and develop a new uapi to >>> solve that, how would we expand this ioctl to support it rather than >>> also create a new ioctl? There's also a trade-off in making the ioctl >>> usage more difficult for the user. I'd still expect the vfio layer to >>> check the flag and interpret data[] as indicated by the flag rather >>> than just passing a blob of opaque data to the iommu layer though. >>> Thanks, >> >> Based on your comments about defining a single ioctl and a unified >> vfio structure (with a @data[] field) for pasid_alloc/free, bind/ >> unbind_gpasid, cache_inv. After some offline trying, I think it would >> be good for bind/unbind_gpasid and cache_inv as both of them use the >> iommu uapi definition. While the pasid alloc/free operation doesn't. >> It would be weird to put all of them together. So pasid alloc/free >> may have a separate ioctl. It would look as below. Does this direction >> look good per your opinion? >> >> ioctl #22: VFIO_IOMMU_PASID_REQUEST >> /** >> * @pasid: used to return the pasid alloc result when flags == ALLOC_PASID >> * specify a pasid to be freed when flags == FREE_PASID >> * @range: specify the allocation range when flags == ALLOC_PASID >> */ >> struct vfio_iommu_pasid_request { >> __u32 argsz; >> #define VFIO_IOMMU_ALLOC_PASID (1 << 0) >> #define VFIO_IOMMU_FREE_PASID (1 << 1) >> __u32 flags; >> __u32 pasid; >> struct { >> __u32 min; >> __u32 max; >> } range; >> }; >> >> ioctl #23: VFIO_IOMMU_NESTING_OP >> struct vfio_iommu_type1_nesting_op { >> __u32 argsz; >> __u32 flags; >> __u32 op; >> __u8 data[]; >> }; >> >> /* Nesting Ops */ >> #define VFIO_IOMMU_NESTING_OP_BIND_PGTBL 0 >> #define VFIO_IOMMU_NESTING_OP_UNBIND_PGTBL 1 >> #define VFIO_IOMMU_NESTING_OP_CACHE_INVLD 2 >> > > Then why cannot we just put PASID into the header since the > majority of nested usage is associated with a pasid? > > ioctl #23: VFIO_IOMMU_NESTING_OP > struct vfio_iommu_type1_nesting_op { > __u32 argsz; > __u32 flags; > __u32 op; > __u32 pasid; > __u8 data[]; > }; > > In case of SMMUv2 which supports nested w/o PASID, this field can > be ignored for that specific case. On my side I would prefer keeping the pasid in the data[]. This is not always used. For instance, in iommu_cache_invalidate_info/iommu_inv_pasid_info we devised flags to tell whether the PASID is used. Thanks Eric > > Thanks > Kevin > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu