From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932814Ab3HNQnZ (ORCPT ); Wed, 14 Aug 2013 12:43:25 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:2555 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760051Ab3HNQnY (ORCPT ); Wed, 14 Aug 2013 12:43:24 -0400 X-IronPort-AV: E=Sophos;i="4.89,878,1367971200"; d="scan'208";a="42146859" Date: Wed, 14 Aug 2013 17:43:22 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Konrad Rzeszutek Wilk CC: Stefano Stabellini , , , , Subject: Re: [PATCH v3 07/10] xen: introduce XENMEM_get_dma_buf and xen_put_dma_buf In-Reply-To: <20130809153606.GD5637@phenom.dumpdata.com> Message-ID: References: <1375720256-8014-7-git-send-email-stefano.stabellini@eu.citrix.com> <20130809153606.GD5637@phenom.dumpdata.com> User-Agent: Alpine 2.02 (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 On Fri, 9 Aug 2013, Konrad Rzeszutek Wilk wrote: > > + * requested. The new pages are going to be "pinned": it's guaranteed > > + * that their p2m mapping won't be changed until explicitly "unpinned". > > What if you try to balloon them out? What happens then? Does that > unpin them automatically? > > What if I use said "pin" page for grants? Can they be shared with another > guest? I'll mention that only normal guest r/w memory can be pinned. > > + * If return code is zero then @out.extent_list provides the MFNs of the > > + * newly-allocated memory. Returns zero on complete success, otherwise > > + * a negative error code. > > Ahem. Which ones? I know you didn't like the existing grant code b/c it > returned some general error. Would it make sense to say which are ones > are expected? I'll do that. > > + * On complete success then always @nr_exchanged == @in.nr_extents. On > > + * partial success @nr_exchanged indicates how much work was done. > > And no error? > > + */ > > +struct xen_get_dma_buf { > > + /* > > + * [IN] Details of memory extents to be exchanged (GMFN bases). > > + * Note that @in.address_bits is ignored and unused. > > Ohhhh, why? What if the user wants to be it under 2G? As per the other email, that goes in out.address_bits. I'll add a note. > > + */ > > + struct xen_memory_reservation in; > > + > > + /* > > + * [IN/OUT] Details of new memory extents. > > + * We require that: > > + * 1. @in.domid == @out.domid > > + * 2. @in.nr_extents << @in.extent_order == > > + * @out.nr_extents << @out.extent_order > > + * 3. @in.extent_start and @out.extent_start lists must not overlap > > + * 4. @out.extent_start lists GPFN bases to be populated > > + * 5. @out.extent_start is overwritten with allocated GMFN bases > > + */ > > + struct xen_memory_reservation out; > > + > > + /* > > + * [OUT] Number of input extents that were successfully exchanged: > > + * 1. The first @nr_exchanged input extents were successfully > > + * deallocated. > > + * 2. The corresponding first entries in the output extent list correctly > > + * indicate the GMFNs that were successfully exchanged. > > + * 3. All other input and output extents are untouched. > > + * 4. If not all input exents are exchanged then the return code of this > > + * command will be non-zero. > > + * 5. THIS FIELD MUST BE INITIALISED TO ZERO BY THE CALLER! > > + */ > > + xen_ulong_t nr_exchanged; > > +}; > > +DEFINE_GUEST_HANDLE_STRUCT(xen_get_dma_buf); > > + > > +#define XENMEM_put_dma_buf 27 > > +/* > > + * XENMEM_put_dma_buf unpins a set of pages, previously pinned by > > + * XENMEM_get_dma_buf. After this call the p2m mapping of the pages can > > + * be transparently changed by the hypervisor, as usual. The pages are > > + * still accessible from the guest. > > I don't understand what 'pinned' means. What is a 'pinned' page versus > a normal page? Is this like the pagetables which must be _RO? A pinned page is just a normal page that the hypervisor promises is going to keep having the same machine address until unpinned.