From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sheng Yang Subject: Re: [PATCH 3/3] KVM: Add documents for MSI-X MMIO API Date: Wed, 26 Jan 2011 17:05:56 +0800 Message-ID: <201101261705.56266.sheng@linux.intel.com> References: <1294309185-21417-1-git-send-email-sheng@linux.intel.com> <201101191621.06840.sheng@linux.intel.com> <4D3EC66A.2050207@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , "Michael S. Tsirkin" , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mga01.intel.com ([192.55.52.88]:32855 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752097Ab1AZJFd (ORCPT ); Wed, 26 Jan 2011 04:05:33 -0500 In-Reply-To: <4D3EC66A.2050207@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tuesday 25 January 2011 20:47:38 Avi Kivity wrote: > On 01/19/2011 10:21 AM, Sheng Yang wrote: > > > > We already got an guest MMIO address for that in the exit > > > > information. I've created a chain of handler in qemu to handle it. > > > > > > But we already decoded the table and entry... > > > > But the handler is still wrapped by vcpu_mmio_write(), as a part of MMIO. > > So it's not quite handy to get the table and entry out. > > The kernel handler can create a new kvm_run exit description. > > > Also the updater in the userspace > > > > can share the most logic with ordinary userspace MMIO handler, which take > > address as parameter. So I think we don't need to pass the decoded > > table_id and entry to userspace. > > It's mixing layers, which always leads to trouble. For one, the user > handler shouldn't do anything with the write since the kernel already > wrote it into the table. For another, if two vcpus write to the same > entry simultaneously, you could see different ordering in the kernel and > userspace, and get inconsistent results. The shared logic is not about writing, but about interpret what's written. Old MMIO handler would write the data, then interpret it; and our new MMIO would only share the logic of interpretation. I think that's fair enough? -- regards Yang, Sheng