From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Hecht Subject: Re: [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot Date: Tue, 13 Feb 2007 18:34:28 -0800 Message-ID: <45D27534.1070608@vmware.com> References: <20070213221729.772002682@goop.org> <20070213221829.845132535@goop.org> <45D2649D.4080508@vmware.com> <45D26797.5090600@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <45D26797.5090600@goop.org> Sender: linux-kernel-owner@vger.kernel.org To: Jeremy Fitzhardinge Cc: Andi Kleen , Andrew Morton , virtualization@lists.osdl.org, xen-devel@lists.xensource.com, Chris Wright , linux-kernel@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org On 02/13/2007 05:36 PM, Jeremy Fitzhardinge wrote: > Dan Hecht wrote: >> Why doesn't Xen allocate the shared_info page from the pseudo-physical >> space? Doesn't it already have to steal pages from the >> pseudo-physical space for e.g. initial page tables, console, etc? Why >> not do the same for shared_info, and then you don't need a reserve the >> fixmap slot. > > Unlike the pagetable pages or the console page, the shared info page > doesn't have a pseudo-physical address, so in order to map it we need to > directly construct a pte containing the mfn for that page. Right. But that is only because Xen decides to allocate the page from the (machine) physical space, rather than from the pseudo-physical space. My question is: why doesn't Xen allocate shared_info from the pseudo-physical space? If it had, then this page wouldn't need to be treated specially. I'm not sure, but I seem to remember on 64-bit Xen/XenLinux allocated shared_info from pseudo-physical space already... Inserting > this mapping into the fixmap space seems like the easiest way to do > this. It's not like a fixmap slot costs anything. > > I don't really have an objection to stealing a fixmap slot, just seems cleaner if you didn't have to special case the shared_info. Dan