Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933494AbdCHCRX (ORCPT ); Tue, 7 Mar 2017 21:17:23 -0500 Received: from mail.kernel.org ([198.145.29.136]:45496 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756434AbdCHCRT (ORCPT ); Tue, 7 Mar 2017 21:17:19 -0500 Date: Tue, 7 Mar 2017 16:49:46 -0800 (PST) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-X260 To: Julien Grall cc: Stefano Stabellini , xen-devel@lists.xenproject.org, jgross@suse.com, Latchesar Ionkov , Eric Van Hensbergen , linux-kernel@vger.kernel.org, Stefano Stabellini , v9fs-developer@lists.sourceforge.net, Ron Minnich , boris.ostrovsky@oracle.com Subject: Re: [Xen-devel] [PATCH 4/7] xen/9pfs: connect to the backend In-Reply-To: Message-ID: References: <1488830488-18506-1-git-send-email-sstabellini@kernel.org> <1488830488-18506-4-git-send-email-sstabellini@kernel.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2828 Lines: 92 On Tue, 7 Mar 2017, Julien Grall wrote: > Hi Stefano, > > On 03/06/2017 08:01 PM, Stefano Stabellini wrote: > > +static int xen_9pfs_front_alloc_dataring(struct xenbus_device *dev, > > + struct xen_9pfs_dataring *ring) > > +{ > > + int i; > > + int ret = -ENOMEM; > > + > > + init_waitqueue_head(&ring->wq); > > + spin_lock_init(&ring->lock); > > + INIT_WORK(&ring->work, p9_xen_response); > > + > > + ring->intf = (struct xen_9pfs_data_intf *) __get_free_page(GFP_KERNEL > > | __GFP_ZERO); > > + if (!ring->intf) > > + goto error; > > + memset(ring->intf, 0, XEN_PAGE_SIZE); > > + ring->bytes = (void*)__get_free_pages(GFP_KERNEL | __GFP_ZERO, > > XEN_9PFS_RING_ORDER); > > The ring order will be in term of Xen page size and not Linux. So you are > going to allocate much more memory than expected on 64KB kernel. I'll fix. > > + if (ring->bytes == NULL) > > + goto error; > > + for (i = 0; i < (1 << XEN_9PFS_RING_ORDER); i++) > > + ring->intf->ref[i] = > > gnttab_grant_foreign_access(dev->otherend_id, > > pfn_to_gfn(virt_to_pfn((void*)ring->bytes) + i), 0);. > > Please use virt_to_gfn rather than pfn_to_gfn(virt_to_pfn). OK > Also, this is not going to work on 64K kernel because you will grant access to > noncontiguous memory (e.g 0-4K, 64K-68K,...). By using virt_to_gfn like you suggested, the loop will correctly iterate on a 4K by 4K basis, even on a 64K kernel: ring->bytes = (void*)__get_free_pages(GFP_KERNEL | __GFP_ZERO, XEN_9PFS_RING_ORDER - (PAGE_SHIFT - XEN_PAGE_SHIFT)); for (i = 0; i < (1 << XEN_9PFS_RING_ORDER); i++) ring->intf->ref[i] = gnttab_grant_foreign_access(dev->otherend_id, virt_to_gfn((void*)ring->bytes) + i, 0); where XEN_9PFS_RING_ORDER specifies the order at 4K granularity. Am I missing something? > We have various helper to break-down the page for you, see > gnttab_for_one_grant, gnttab_foreach_grant, gnttab_count_grant, > xen_for_each_gfn (though this one it is internal to xlate_mmu.c so far) > > Please use them to avoid any further. > > > + ring->ref = gnttab_grant_foreign_access(dev->otherend_id, > > pfn_to_gfn(virt_to_pfn((void*)ring->intf)), 0); > > Please use virt_to_gfn rather than pfn_to_gfn(virt_to_pfn). Sure > > + ring->ring.in = ring->bytes; > > + ring->ring.out = ring->bytes + XEN_9PFS_RING_SIZE; > > + > > + ret = xenbus_alloc_evtchn(dev, &ring->evtchn); > > + if (ret) > > + goto error; > > + ring->irq = bind_evtchn_to_irqhandler(ring->evtchn, > > xen_9pfs_front_event_handler, > > + 0, "xen_9pfs-frontend", ring); > > + if (ring->irq < 0) { > > + xenbus_free_evtchn(dev, ring->evtchn); > > + ret = ring->irq; > > + goto error; > > + } > > return 0; > > + > > +error: > > + if (ring->intf != NULL) > > + kfree(ring->intf); > > + if (ring->bytes != NULL) > > + kfree(ring->bytes); > > + return ret; > > }