From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Userspace hypercalls? Date: Mon, 27 Aug 2007 20:36:46 +0300 Message-ID: <46D30BAE.4080705@qumranet.com> References: <1188228447.12698.8.camel@squirrel> <46D2F8FA.6050104@qumranet.com> <46D2FCE1.7020605@qumranet.com> <46D3001A.9070706@qumranet.com> <1188235942.6364.12.camel@squirrel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Anthony Liguori Return-path: In-Reply-To: <1188235942.6364.12.camel@squirrel> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Anthony Liguori wrote: > On Mon, 2007-08-27 at 19:47 +0300, Avi Kivity wrote: > >> Avi Kivity wrote: >> >>> Thinking a little more about this, it isn't about handling hypercalls >>> in userspace, but about handling a virtio sync() in userspace. >>> >>> So how about having a KVM_HC_WAKE_CHANNEL hypercall (similar to Xen's >>> event channel, but assymetric) that has a channel parameter. The >>> kernel handler for that hypercall dispatches calls to either a kernel >>> handler or a userspace handler. That means we don't need a separate >>> ETH_SEND, ETH_RECEIVE, or BLOCK_SEND hypercalls. >>> >> And thinking a tiny little bit more about this, we can have the kernel >> (optionally) fire an eventfd, so a separate userspace thread or process >> can be woken up to service the device, without a heavyweight exit. >> > > > Yes, I think this is much nicer. By "calls to ... a userspace handler" > I presume you mean generating an exit to userspace with a new exit type > similar to how hypercalls work today? > > There are two options: - hypercall handler sets some fields in vcpu->run and exits to userspace - hypercall handler triggers an eventfd and returns to guest Maybe we can unify the two by only allowing eventfd; userspace can attach a signal to the eventfd if it wants a synchronous exit (does eventfd allow fcntl(F_SETOWN)?) -- Any sufficiently difficult bug is indistinguishable from a feature. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/