From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stanislaw Gruszka Subject: Re: MT76x2U crashes XHCI driver on AMD Ryzen system Date: Thu, 28 Feb 2019 10:04:12 +0100 Message-ID: <20190228090411.GA24938@redhat.com> References: <20190114091841.GA23045@localhost.localdomain> <20190115090400.GA2267@localhost.localdomain> <20190218143742.GA11872@redhat.com> <20190226100535.GA20740@8bytes.org> <20190226103450.GA2989@redhat.com> <20190226104413.GH20740@8bytes.org> <20190226112407.GB2989@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190226112407.GB2989@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Joerg Roedel Cc: Lorenzo Bianconi , Rosen Penev , linux-wireless , Samuel Sieb , Alexander Duyck , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org On Tue, Feb 26, 2019 at 12:24:08PM +0100, Stanislaw Gruszka wrote: > On Tue, Feb 26, 2019 at 11:44:13AM +0100, Joerg Roedel wrote: > > On Tue, Feb 26, 2019 at 11:34:51AM +0100, Stanislaw Gruszka wrote: > > > On Tue, Feb 26, 2019 at 11:05:36AM +0100, Joerg Roedel wrote: > > > If sg->offset > PAGE_SIZE is fine then most likely we have problem with > > > alignment. > > > > The map_sg implementation in the AMD IOMMU driver uses sg_phys() which > > handles the sg->page + sg->offset calculation fine. > > > > > Note hat issue is with dma_map_sg(), switching to dma_map_single() > > > by using urb->transfer_buffer instead of urb->sg make things work > > > on AMD IOMMU. > > > > On the other hand this points to a bug in the driver, I'll look further > > if I can spot something there. > > I think so too. And I have done some changes that avoid strange allocation > scheme and use usb synchronous messages instead of allocating buffers > with unaligned sizes. However things work ok on Intel IOMMU and > there is no documentation what are dma_map_sg() requirement versus > dma_map_single() which works. I think there are some unwritten > requirements and things can work on some platforms and fails on others > (different IOMMUs, no-IOMMU on some ARCHes) For the record: we have another bug report with this issue: https://bugzilla.kernel.org/show_bug.cgi?id=202673 I provided there patch that change alignment for page_frag_alloc() and it did not fixed the problem. So this is not alignment issue. Now I think it could be page->refcount issue ... Stanislaw