From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCHv5 3/3] vhost_net: a kernel-level virtio server Date: Mon, 14 Sep 2009 19:53:20 +0300 Message-ID: <20090914165320.GA3851@redhat.com> References: <20090827160750.GD23722@redhat.com> <20090903183945.GF28651@ovro.caltech.edu> <20090907101537.GH3031@redhat.com> <20090908172035.GB319@ovro.caltech.edu> <4AAA7415.5080204@gmail.com> <20090913120140.GA31218@redhat.com> <4AAE6A97.7090808@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Ira W. Snyder" , netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, linux-mm@kvack.org, akpm@linux-foundation.org, hpa@zytor.com, Rusty Russell , s.hetze@linux-ag.com To: Gregory Haskins Return-path: Content-Disposition: inline In-Reply-To: <4AAE6A97.7090808@gmail.com> Sender: owner-linux-mm@kvack.org List-Id: netdev.vger.kernel.org On Mon, Sep 14, 2009 at 12:08:55PM -0400, Gregory Haskins wrote: > Michael S. Tsirkin wrote: > > On Fri, Sep 11, 2009 at 12:00:21PM -0400, Gregory Haskins wrote: > >> FWIW: VBUS handles this situation via the "memctx" abstraction. IOW, > >> the memory is not assumed to be a userspace address. Rather, it is a > >> memctx-specific address, which can be userspace, or any other type > >> (including hardware, dma-engine, etc). As long as the memctx knows how > >> to translate it, it will work. > > > > How would permissions be handled? > > Same as anything else, really. Read on for details. > > > it's easy to allow an app to pass in virtual addresses in its own address space. > > Agreed, and this is what I do. > > The guest always passes its own physical addresses (using things like > __pa() in linux). This address passed is memctx specific, but generally > would fall into the category of "virtual-addresses" from the hosts > perspective. > > For a KVM/AlacrityVM guest example, the addresses are GPAs, accessed > internally to the context via a gfn_to_hva conversion (you can see this > occuring in the citation links I sent) > > For Ira's example, the addresses would represent a physical address on > the PCI boards, and would follow any kind of relevant rules for > converting a "GPA" to a host accessible address (even if indirectly, via > a dma controller). So vbus can let an application access either its own virtual memory or a physical memory on a PCI device. My question is, is any application that's allowed to do the former also granted rights to do the later? > > But we can't let the guest specify physical addresses. > > Agreed. Neither your proposal nor mine operate this way afaict. > > HTH > > Kind Regards, > -Greg > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org