From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:13270 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726808AbfK2OJw (ORCPT ); Fri, 29 Nov 2019 09:09:52 -0500 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xATE2aZF051082 for ; Fri, 29 Nov 2019 09:09:51 -0500 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0a-001b2d01.pphosted.com with ESMTP id 2wjuwh9t0v-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Fri, 29 Nov 2019 09:09:51 -0500 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 29 Nov 2019 14:09:48 -0000 Date: Fri, 29 Nov 2019 15:09:41 +0100 From: Halil Pasic Subject: Re: [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails In-Reply-To: <20191126184527.GA10481@lst.de> References: <20191114124646.74790-1-pasic@linux.ibm.com> <20191119121022.03aed69a.pasic@linux.ibm.com> <20191119080420-mutt-send-email-mst@kernel.org> <20191122140827.0ead345c.pasic@linux.ibm.com> <1ec7c229-6c4f-9351-efda-ed2df20f95f6@amd.com> <20191126184527.GA10481@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20191129150941.34cab07a.pasic@linux.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christoph Hellwig Cc: Tom Lendacky , "Michael S. Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Cornelia Huck , linux-s390@vger.kernel.org, Michael Mueller , Christian Borntraeger , Janosch Frank , Ram Pai , Thiago Jung Bauermann , Andy Lutomirski , Brijesh Singh , "Kalra, Ashish" On Tue, 26 Nov 2019 19:45:27 +0100 Christoph Hellwig wrote: > On Sat, Nov 23, 2019 at 09:39:08AM -0600, Tom Lendacky wrote: > > Ideally, having a pool of shared pages for DMA, outside of standard > > SWIOTLB, might be a good thing. On x86, SWIOTLB really seems geared > > towards devices that don't support 64-bit DMA. If a device supports 64-bit > > DMA then it can use shared pages that reside anywhere to perform the DMA > > and bounce buffering. I wonder if the SWIOTLB support can be enhanced to > > support something like this, using today's low SWIOTLB buffers if the DMA > > mask necessitates it, otherwise using a dynamically sized pool of shared > > pages that can live anywhere. > > I think that can be done relatively easily. I've actually been thinking > of multiple pool support for a whіle to replace the bounce buffering > in the block layer for ISA devices (24-bit addressing). > > I've also been looking into a dma_alloc_pages interface to help people > just allocate pages that are always dma addressable, but don't need > a coherent allocation. My last version I shared is here: > > http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma_alloc_pages > > But it turns out this still doesn't work with SEV as we'll always > bounce. And I've been kinda lost on figuring out a way how to > allocate unencrypted pages that we we can feed into the normal > dma_map_page & co interfaces due to the magic encryption bit in > the address. I guess we could have a fallback path in the mapping > path and just unconditionally clear that bit in the dma_to_phys > path. Thanks Christoph! Thanks Tom! I will do some looking and thinking and report back. Regards, Halil