From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH] KVM: optimize apic interrupt delivery Date: Tue, 11 Sep 2012 15:04:36 +0300 Message-ID: <504F28D4.4050105@redhat.com> References: <20120910130915.GB20907@redhat.com> <20120910144438.GA19741@redhat.com> <20120910161754.GB25827@redhat.com> <20120910170522.GC25827@redhat.com> <504F0462.5050103@redhat.com> <20120911093502.GF20907@redhat.com> <504F0748.5010705@redhat.com> <20120911094546.GA23020@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , kvm@vger.kernel.org, mtosatti@redhat.com To: Gleb Natapov Return-path: Received: from mx1.redhat.com ([209.132.183.28]:33864 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454Ab2IKMEl (ORCPT ); Tue, 11 Sep 2012 08:04:41 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q8BC4egD028446 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 11 Sep 2012 08:04:40 -0400 In-Reply-To: <20120911094546.GA23020@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/11/2012 12:45 PM, Gleb Natapov wrote: >> >> >> > There is no userspace to return error to if error happens on guest MMIO >> > write. Unless you mean return it as a return value of ioctl(VM_RUN) in >> > which case it is equivalent of killing the guest. >> >> That is what I meant. >> >> > And this is not fair >> > to a guest who did nothing wrong to suffer from our stupid optimizations :) >> > Actually I am not sure that returning to userspace in the middle of an >> > IO that is handled by a kernel is well defined in KVM ABI. >> >> If you get -ENOMEM when allocating a page without GFP_ATOMIC (or >> GFP_NOIO etc) then the entire host is dead anyway. The same thing can >> happen if the guest (or userspace) touches a yet-unallocated page, or if >> the page fault path fails to allocate mmu pages, or any of a thousand >> other allocations we have all over. > Then it is just simpler to sigkill the guest right away. What's the > point in returning error if you believe that userspace can't handle it > and will likely not run long enough to even get to userspace due to > memory shortage. Syscalls don't SIGKILL (well except kill(2)). They report errors. The only other alternative is SIGBUS. > >> >> > >> >> >> >> >> > Actually I have an idea how to handle the error. Never return one. If >> >> > map cannot be allocated go slow path always. phys_map should be checked >> >> > for NULL during delivery in this case obviously. >> >> >> >> That's better of course (though we have to beware of such tricks, but in >> >> this case the slow path is regularly exercised so it should keep working). >> >> >> > Oh with Windows guests it has work to do for sure. >> >> This reminds me, we could speed up self-ipi for that. >> > The patch does it. Windows sends a lot of all but self IPIs too. I thought it bailed out if a destination shorthand was used? -- error compiling committee.c: too many arguments to function