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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id gn36sm1982567ejc.23.2021.05.04.14.56.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 May 2021 14:56:30 -0700 (PDT) Subject: Re: [PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry To: Sean Christopherson Cc: Andy Lutomirski , Maxim Levitsky , Thomas Gleixner , Lai Jiangshan , linux-kernel@vger.kernel.org, Lai Jiangshan , Steven Rostedt , Andi Kleen , Andy Lutomirski , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Josh Poimboeuf , Uros Bizjak , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Alexandre Chartre , Juergen Gross , Joerg Roedel , Jian Cai References: <38B9D60F-F24F-4910-B2DF-2A57F1060452@amacapital.net> <625057c7-ea40-4f37-8bea-cddecfe1b855@redhat.com> From: Paolo Bonzini Message-ID: <5d7ca301-a0b2-d389-3bc2-feb304c9f5b5@redhat.com> Date: Tue, 4 May 2021 23:56:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/05/21 23:51, Sean Christopherson wrote: > On Tue, May 04, 2021, Paolo Bonzini wrote: >> On 04/05/21 23:23, Andy Lutomirski wrote: >>>> On May 4, 2021, at 2:21 PM, Sean Christopherson wrote: >>>> FWIW, NMIs are masked if the VM-Exit was due to an NMI. >> >> Huh, indeed: "An NMI causes subsequent NMIs to be blocked, but only after >> the VM exit completes". >> >>> Then this whole change is busted, since nothing will unmask NMIs. Revert it? >> Looks like the easiest way out indeed. > > I've no objection to reverting to intn, but what does reverting versus handling > NMI on the kernel stack have to do with NMIs being blocked on VM-Exit due to NMI? > I'm struggling mightily to connect the dots. Nah, you're right: vmx_do_interrupt_nmi_irqoff will not call the handler directly, rather it calls the IDT entrypoint which *will* do an IRET and unmask NMIs. I trusted Andy too much on this one. :) Thomas's posted patch ("[PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry") looks good. Paolo