linux-kernel - Re: [PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry

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Message-ID: <ae801539-592a-af9a-55a1-3a4b8309ff1e@redhat.com>
Date:   Tue, 4 May 2021 23:12:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Uros Bizjak <ubizjak@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Joerg Roedel <jroedel@...e.de>, Jian Cai <caij2003@...il.com>
Subject: Re: [PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry

On 04/05/21 23:05, Maxim Levitsky wrote:
> Does this mean that we still rely on hardware NMI masking to be activated?

No, the NMI code already handles reentrancy at both the assembly and C 
levels.

> Or in other words, that is we still can't have an IRET between VM exit and
> the entry to the NMI handler?

No, because NMIs are not masked on VM exit.  This in fact makes things 
potentially messy; unlike with AMD's CLGI/STGI, only MSRs and other 
things that Intel thought can be restored atomically with the VM exit.

Paolo