From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mailout2.w1.samsung.com ([210.118.77.12]:23687 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751809Ab3KYPlq (ORCPT ); Mon, 25 Nov 2013 10:41:46 -0500 MIME-version: 1.0 Content-type: text/plain; charset=UTF-8; format=flowed Received: from eucpsbgm2.samsung.com (unknown [203.254.199.245]) by mailout2.w1.samsung.com (Oracle Communications Messaging Server 7u4-24.01(7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0MWT00BQHSXJMU70@mailout2.w1.samsung.com> for linux-media@vger.kernel.org; Mon, 25 Nov 2013 15:41:44 +0000 (GMT) Content-transfer-encoding: 8BIT Message-id: <52936FB7.9030307@samsung.com> Date: Mon, 25 Nov 2013 16:41:43 +0100 From: Marek Szyprowski To: =?UTF-8?B?TWF0dGhpYXMgV8OkY2h0ZXI=?= , Ricardo Ribalda Delgado , Pawel Osciak , Kyungmin Park , Mauro Carvalho Chehab , "open list:VIDEOBUF2 FRAMEWORK" , "sylvester.nawrocki@gmail.com" Subject: Re: [PATCH] videobuf2-dma-sg: Support io userptr operations on io memory References: <1383767329-29985-1-git-send-email-ricardo.ribalda@gmail.com> <3377d5e29bf6444086575515325b3555@TTTEX01.ds1.internal> In-reply-to: <3377d5e29bf6444086575515325b3555@TTTEX01.ds1.internal> Sender: linux-media-owner@vger.kernel.org List-ID: Hello, On 2013-11-11 12:36, Matthias Wächter wrote: > > @@ -180,7 +186,26 @@ static void *vb2_dma_sg_get_userptr(void > > *alloc_ctx, unsigned long vaddr, > > if (!buf->pages) > > return NULL; > > > > - num_pages_from_user = get_user_pages(current, current->mm, > > + buf->vma = find_vma(current->mm, vaddr); > > + if (!buf->vma) { > > + dprintk(1, "no vma for address %lu\n", vaddr); > > + return NULL; > > + } > > + > > + if (vma_is_io(buf->vma)) { > > + for (num_pages_from_user = 0; > > + num_pages_from_user < buf->num_pages; > > + ++num_pages_from_user, vaddr += PAGE_SIZE) { > > + unsigned long pfn; > > + > > + if (follow_pfn(buf->vma, vaddr, &pfn)) { > > + dprintk(1, "no page for address %lu\n", vaddr); > > + break; > > + } > > + buf->pages[num_pages_from_user] = pfn_to_page(pfn); > > + } > > + } else > > + num_pages_from_user = get_user_pages(current, current->mm, > > vaddr & PAGE_MASK, > > buf->num_pages, > > write, > > Can you safely assume that your userptr will cover only one vma? At least, get_user_pages (calling __get_user_pages) does not assume that and calls find_vma() whenever vma->vm_end is reached. We care only about io mappings which cover only one vma. Such mappings are created by other device drivers and can be used mainly for zero-copy buffer sharing between multimedia devices. Although it is technically possible to provide code for multiple vma, there will be no real use case for it. Best regards -- Marek Szyprowski Samsung R&D Institute Poland