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Date: Wed, 13 May 2020 18:35:40 -0700 From: Andy Lutomirski <luto@...capital.net> To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> Cc: rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>, paulmck <paulmck@...nel.org>, Alexandre Chartre <alexandre.chartre@...cle.com>, Frederic Weisbecker <frederic@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Masami Hiramatsu <mhiramat@...nel.org>, Petr Mladek <pmladek@...e.com>, "Joel Fernandes, Google" <joel@...lfernandes.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Juergen Gross <JGross@...e.com>, Brian Gerst <brgerst@...il.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Will Deacon <will@...nel.org> Subject: Re: [patch V4 part 3 01/29] x86/traps: Mark fixup_bad_iret() noinstr > On May 13, 2020, at 5:41 PM, Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote: > > ----- On May 12, 2020, at 9:51 PM, rostedt rostedt@...dmis.org wrote: > >>> On Fri, 8 May 2020 17:39:00 -0700 >>> Andy Lutomirski <luto@...nel.org> wrote: >>> >>> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@...utronix.de> wrote: >>>> >>>> This is called from deep entry ASM in a situation where instrumentation >>>> will cause more harm than providing useful information. >>>> >>> >>> Acked-by: Andy Lutomirski <luto@...nel.org> >>> >>> Maybe add to changelog: >>> >>> Switch from memmove() to memcpy() because memmove() can't be called >>> from noinstr code. >> >> Yes please, because I was about to say that there was changes that >> didn't seem to fit the change log. >> >> I would also add a comment in the code saying that we need the temp >> variable to use memcpy as memmove can't be used in noinstr code. > > Looking at an updated version of the tree, I see the acked-by from Andy, > but not comment about switching from memmove to memcpy. > > Also, I notice a significant undocumented change in this patch: it changes > a this_cpu_read() (which presumes preemption is enabled) to a __this_cpu_read(). > > So the 100$ question: is preemption enabled or not in fixup_bad_iret() ? And of > course that change should be documented in the commit message. > IRQs are off, and, if they were on, the lack of a warning from the percpu access would be the least of our concerns here. > Thanks, > > Mathieu > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com
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