From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot1-f71.google.com (mail-ot1-f71.google.com [209.85.210.71]) by kanga.kvack.org (Postfix) with ESMTP id 709896B3F91 for ; Mon, 26 Nov 2018 08:18:59 -0500 (EST) Received: by mail-ot1-f71.google.com with SMTP id 73so8528977oth.9 for ; Mon, 26 Nov 2018 05:18:59 -0800 (PST) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id e17si149921oib.145.2018.11.26.05.18.58 for ; Mon, 26 Nov 2018 05:18:58 -0800 (PST) Subject: Re: [PATCH 6/9] iommu/dma-iommu.c: Convert to use vm_insert_range References: <20181115154950.GA27985@jordon-HP-15-Notebook-PC> <20181123213448.GW3065@bombadil.infradead.org> From: Robin Murphy Message-ID: <7a3e53dc-9949-5b33-1282-54ae8ac1c62f@arm.com> Date: Mon, 26 Nov 2018 13:18:53 +0000 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Souptick Joarder , Matthew Wilcox Cc: Andrew Morton , Michal Hocko , joro@8bytes.org, Linux-MM , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org On 26/11/2018 06:44, Souptick Joarder wrote: > On Sat, Nov 24, 2018 at 3:04 AM Matthew Wilcox wrote: >> >> On Fri, Nov 23, 2018 at 05:23:06PM +0000, Robin Murphy wrote: >>> On 15/11/2018 15:49, Souptick Joarder wrote: >>>> Convert to use vm_insert_range() to map range of kernel >>>> memory to user vma. >>>> >>>> Signed-off-by: Souptick Joarder >>>> Reviewed-by: Matthew Wilcox >>>> --- >>>> drivers/iommu/dma-iommu.c | 12 ++---------- >>>> 1 file changed, 2 insertions(+), 10 deletions(-) >>>> >>>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >>>> index d1b0475..69c66b1 100644 >>>> --- a/drivers/iommu/dma-iommu.c >>>> +++ b/drivers/iommu/dma-iommu.c >>>> @@ -622,17 +622,9 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp, >>>> int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma) >>>> { >>>> - unsigned long uaddr = vma->vm_start; >>>> - unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT; >>>> - int ret = -ENXIO; >>>> + unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT; >>>> - for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) { >>>> - ret = vm_insert_page(vma, uaddr, pages[i]); >>>> - if (ret) >>>> - break; >>>> - uaddr += PAGE_SIZE; >>>> - } >>>> - return ret; >>>> + return vm_insert_range(vma, vma->vm_start, pages, count); >>> >>> AFIACS, vm_insert_range() doesn't respect vma->vm_pgoff, so doesn't this >>> break partial mmap()s of a large buffer? (which I believe can be a thing) >> >> Whoops. That should have been: >> >> return vm_insert_range(vma, vma->vm_start, pages + vma->vm_pgoff, count); > > I am unable to trace back where vma->vm_pgoff is set for this driver ? if any ? This isn't a driver - it's a DMA API backend, so any caller of dma_mmap_*() could potentially end up here (similarly for patch 2/9). Robin. > If default value set to 0 then I think existing code is correct. > >> >> I suppose. >> > >> Although arguably we should respect vm_pgoff inside vm_insert_region() >> and then callers automatically get support for vm_pgoff without having >> to think about it ... > > I assume, vm_insert_region() means vm_insert_range(). If we respect vm_pgoff > inside vm_insert_range, for any uninitialized/ error value set for vm_pgoff from > drivers will introduce a bug inside core mm which might be difficult > to trace back. > But when vm_pgoff set and passed from caller (drivers) it might be > easy to figure out. > >> although we should then also pass in the length >> of the pages array to avoid pages being mapped in which aren't part of >> the allocated array. > > Mostly Partial mapping is done by starting from an index and mapped it till > end of pages array. Calculating length of the pages array will have a small > overhead for each drivers. > > Please correct me if I am wrong. >