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([2601:642:c400:7877:8ce1:4e59:b8f:be36]) by smtp.gmail.com with ESMTPSA id v75sm10743292pfa.164.2019.02.15.10.28.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 15 Feb 2019 10:28:09 -0800 (PST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch From: Andy Lutomirski X-Mailer: iPhone Mail (16C101) In-Reply-To: <20190215174034.GP32494@hirez.programming.kicks-ass.net> Date: Fri, 15 Feb 2019 10:28:08 -0800 Cc: Linus Torvalds , Brian Gerst , Julien Thierry , Will Deacon , Ingo Molnar , Linux Kernel Mailing List , "linux-alpha@vger.kernel.org" , Ingo Molnar , Catalin Marinas , James Morse , "H. Peter Anvin" , valentin.schneider@arm.com, Josh Poimboeuf , Andy Lutomirski , Borislav Petkov , Denys Vlasenko , Thomas Gleixner Content-Transfer-Encoding: quoted-printable Message-Id: References: <20190213144145.GY32494@hirez.programming.kicks-ass.net> <20190213154532.GQ32534@hirez.programming.kicks-ass.net> <20190213222146.GC32494@hirez.programming.kicks-ass.net> <20190214101429.GD32494@hirez.programming.kicks-ass.net> <20190214193432.GR32477@hirez.programming.kicks-ass.net> <20190215174034.GP32494@hirez.programming.kicks-ass.net> To: Peter Zijlstra Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Feb 15, 2019, at 9:40 AM, Peter Zijlstra wrote: >=20 >> On Fri, Feb 15, 2019 at 09:18:00AM -0800, Linus Torvalds wrote: >>> On Thu, Feb 14, 2019 at 11:34 AM Peter Zijlstra w= rote: >>>=20 >>> Something like the below, right? >>>=20 >>> + frame->flags =3D 0; >>> + frame->flags =3D 0; >>=20 >> Those are not valid flag values. >>=20 >> Can you popf them? Yes. >>=20 >> Do they make sense? No. >>=20 >> It has the IF flag clear, for example. Is that intentional? If it is, >=20 > Uhmm. yeah, that's bonkers. We should have interrupts disabled here. > I'll go read up on the eflags and figure out what they _should_ be right > about there. And probably add a comment near the POPF explaining that it will keep IRQs o= ff :)=