From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH 1/4] x86 paravirt_ops: create no_paravirt.h for native ops Date: Sun, 06 Aug 2006 23:23:49 -0700 Message-ID: <44D6DC75.90203@goop.org> References: <1154925835.21647.29.camel@localhost.localdomain> <200608070730.17813.ak@muc.de> <44D6D315.2030907@goop.org> <200608070802.40614.ak@muc.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200608070802.40614.ak@muc.de> Sender: linux-kernel-owner@vger.kernel.org To: Andi Kleen Cc: virtualization@lists.osdl.org, Andrew Morton , Linux Kernel Mailing List , Chris Wright List-Id: virtualization@lists.linuxfoundation.org Andi Kleen wrote: >> so it would be >> nice to use one of the other serializing instructions in this case. >> > > You would first need to find one that works in ring 3. On x86-64 it is > used in the gettimeoday vsyscall in ring 3 to synchronize the TSC and > afaik John was about to implement that for i386 too. > Well, that's really usermode code, so I don't think we'd necessarily touch it at all. It's not the same problem as the (single, at the moment) ring 0 use. > BTW another issue that I haven't checked but we will need to make > this also an alternative() for another case - it is faily important > to patch it out on Intel systems with a synchronized TSC where it is > fairly expensive. That is also not done yet on i386, but will be > likely once vsyscall gettimeofday is implemented. > > So basically you would need double patching. Ugly. > Yeah. I guess the cleanest way to do that is do the paravirt substitution, and then nop it out later if it isn't needed in the vsyscall. > I would recommend to keep it out of para ops. It's hardly a big deal either way. There's only one in-kernel use of it. J