From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:52662 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932635AbcDLNa3 (ORCPT ); Tue, 12 Apr 2016 09:30:29 -0400 Date: Tue, 12 Apr 2016 15:30:23 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Greg Kroah-Hartman Cc: Ben Hutchings , Yuki Shibuya , Paolo Bonzini , stable Subject: Re: [PATCH 4.5 007/238] KVM: i8254: change PIT discard tick policy Message-ID: <20160412133023.GA3696@potion.brq.redhat.com> References: <1460417015.25201.67.camel@decadent.org.uk> <20160412012135.GA11311@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20160412012135.GA11311@kroah.com> Sender: stable-owner@vger.kernel.org List-ID: 2016-04-11 18:21-0700, Greg Kroah-Hartman: > On Tue, Apr 12, 2016 at 12:23:35AM +0100, Ben Hutchings wrote: > > On Wed, 2016-03-02 at 22:56 +0100, Radim Krčmář wrote: >> > Even though there is a chance of regressions, I think we can fix the >> > LVT0 NMI bug without introducing a new tick policy. >> [...] >> >> Given the 'chance of regressions', should we let this sit in mainline >> longer before including it in stable updates? > > Hm, good point, Radim, what do you think, is this good to go to stable > now? This has been in since 4.6-rc1, so it's been a few weeks with > people running it already... I think it is good to go. No reasonable workload should regress and the fixed use-case is common on old linux guest. This patch makes a difference if the guest doesn't EOI in PIT interrupts before the next one arrives. PIT would have been unreliable in that situation, so all worloads that that could regress have likely been avoided. Changes to NMI injection would need even crazier guest to regress. (This patch always injects NMI from PIT and shrinks a window where a maskable PIT interrupt is discarded. Previously, next interrupt would have been discarded as long as the last one is in IRR or ISR. Only IRR is considered after this patch, so PIT interrupts are more likely to chain.)