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([2601:646:c200:1ef2:54d3:a29c:f391:9a0d]) by smtp.gmail.com with ESMTPSA id y14sm12278847pfp.127.2020.04.06.13.32.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Apr 2020 13:32:02 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS Date: Mon, 6 Apr 2020 13:32:01 -0700 Message-Id: <6875DD55-2408-4216-B32A-9487A4FDEFD8@amacapital.net> References: <20200406202505.GO2452@worktop.programming.kicks-ass.net> Cc: Vivek Goyal , Thomas Gleixner , Andy Lutomirski , Paolo Bonzini , LKML , X86 ML , kvm list , stable In-Reply-To: <20200406202505.GO2452@worktop.programming.kicks-ass.net> To: Peter Zijlstra X-Mailer: iPhone Mail (17E255) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Apr 6, 2020, at 1:25 PM, Peter Zijlstra wrote: >=20 > =EF=BB=BFOn Mon, Apr 06, 2020 at 03:09:51PM -0400, Vivek Goyal wrote: >>> On Mon, Mar 09, 2020 at 09:22:15PM +0100, Peter Zijlstra wrote: >>> On Mon, Mar 09, 2020 at 08:05:18PM +0100, Thomas Gleixner wrote: >>>> Andy Lutomirski writes: >>>=20 >>>>> I'm okay with the save/restore dance, I guess. It's just yet more >>>>> entry crud to deal with architecture nastiness, except that this >>>>> nastiness is 100% software and isn't Intel/AMD's fault. >>>>=20 >>>> And we can do it in C and don't have to fiddle with it in the ASM >>>> maze. >>>=20 >>> Right; I'd still love to kill KVM_ASYNC_PF_SEND_ALWAYS though, even if >>> we do the save/restore in do_nmi(). That is some wild brain melt. Also, >>> AFAIK none of the distros are actually shipping a PREEMPT=3Dy kernel >>> anyway, so killing it shouldn't matter much. >>=20 >> It will be nice if we can retain KVM_ASYNC_PF_SEND_ALWAYS. I have another= >> use case outside CONFIG_PREEMPT. >>=20 >> I am trying to extend async pf interface to also report page fault errors= >> to the guest. >=20 > Then please start over and design a sane ParaVirt Fault interface. The > current one is utter crap. Agreed. Don=E2=80=99t extend the current mechanism. Replace it. I would be happy to review a replacement. I=E2=80=99m not really excited to r= eview an extension of the current mess. The current thing is barely, if at a= ll, correct.=