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Fri, 08 Jun 2018 19:17:35 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w58JHXrs004218 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 8 Jun 2018 19:17:34 GMT Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w58JHWmo023284; Fri, 8 Jun 2018 19:17:32 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 08 Jun 2018 12:17:32 -0700 Subject: Re: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers To: Stefano Stabellini , Oleksandr Andrushchenko Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, jgross@suse.com, konrad.wilk@oracle.com, daniel.vetter@intel.com, matthew.d.roper@intel.com, dongwon.kim@intel.com, Oleksandr Andrushchenko , julien.grall@arm.com References: <20180601114132.22596-1-andr2000@gmail.com> <20180601114132.22596-6-andr2000@gmail.com> <64facf05-0a51-c3d9-9d3b-780893248628@oracle.com> <84217eac-b83b-710f-39ab-c93cad65bf9a@gmail.com> <30fa03c0-1b75-c0b1-b14f-8b52ea584e20@gmail.com> <78dc2fc4-cdac-05b7-2c34-22b69e7e009c@oracle.com> <4be24882-185d-01e3-6aa1-751e341433c7@gmail.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8918 signatures=668702 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1805220000 definitions=main-1806080211 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/08/2018 01:59 PM, Stefano Stabellini wrote: > >>>>>>>>    @@ -325,6 +401,14 @@ static int map_grant_pages(struct >>>>>>>> grant_map >>>>>>>> *map) >>>>>>>>            map->unmap_ops[i].handle = map->map_ops[i].handle; >>>>>>>>            if (use_ptemod) >>>>>>>>                map->kunmap_ops[i].handle = >>>>>>>> map->kmap_ops[i].handle; >>>>>>>> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC >>>>>>>> +        else if (map->dma_vaddr) { >>>>>>>> +            unsigned long mfn; >>>>>>>> + >>>>>>>> +            mfn = __pfn_to_mfn(page_to_pfn(map->pages[i])); >>>>>>> Not pfn_to_mfn()? >>>>>> I'd love to, but pfn_to_mfn is only defined for x86, not ARM: [1] >>>>>> and [2] >>>>>> Thus, >>>>>> >>>>>> drivers/xen/gntdev.c:408:10: error: implicit declaration of function >>>>>> ‘pfn_to_mfn’ [-Werror=implicit-function-declaration] >>>>>>      mfn = pfn_to_mfn(page_to_pfn(map->pages[i])); >>>>>> >>>>>> So, I'll keep __pfn_to_mfn >>>>> How will this work on non-PV x86? >>>> So, you mean I need: >>>> #ifdef CONFIG_X86 >>>> mfn = pfn_to_mfn(page_to_pfn(map->pages[i])); >>>> #else >>>> mfn = __pfn_to_mfn(page_to_pfn(map->pages[i])); >>>> #endif >>>> >>> I'd rather fix it in ARM code. Stefano, why does ARM uses the >>> underscored version? >> Do you want me to add one more patch for ARM to wrap __pfn_to_mfn >> with static inline for ARM? e.g. >> static inline ...pfn_to_mfn(...) >> { >>     __pfn_to_mfn(); >> } > > A Xen on ARM guest doesn't actually know the mfns behind its own > pseudo-physical pages. This is why we stopped using pfn_to_mfn and > started using pfn_to_bfn instead, which will generally return "pfn", > unless the page is a foreign grant. See include/xen/arm/page.h. > pfn_to_bfn was also introduced on x86. For example, see the usage of > pfn_to_bfn in drivers/xen/swiotlb-xen.c. Otherwise, if you don't care > about other mapped grants, you can just use pfn_to_gfn, that always > returns pfn. I think then this code needs to use pfn_to_bfn(). > > Also, for your information, we support different page granularities in > Linux as a Xen guest, see the comment at include/xen/arm/page.h: > > /* > * The pseudo-physical frame (pfn) used in all the helpers is always based > * on Xen page granularity (i.e 4KB). > * > * A Linux page may be split across multiple non-contiguous Xen page so we > * have to keep track with frame based on 4KB page granularity. > * > * PV drivers should never make a direct usage of those helpers (particularly > * pfn_to_gfn and gfn_to_pfn). > */ > > A Linux page could be 64K, but a Xen page is always 4K. A granted page > is also 4K. We have helpers to take into account the offsets to map > multiple Xen grants in a single Linux page, see for example > drivers/xen/grant-table.c:gnttab_foreach_grant. Most PV drivers have > been converted to be able to work with 64K pages correctly, but if I > remember correctly gntdev.c is the only remaining driver that doesn't > support 64K pages yet, so you don't have to deal with it if you don't > want to. I believe somewhere in this series there is a test for PAGE_SIZE vs. XEN_PAGE_SIZE. Right, Oleksandr? Thanks for the explanation. -boris