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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry
Date:   Tue, 4 May 2021 14:23:37 -0700
Message-Id: <38B9D60F-F24F-4910-B2DF-2A57F1060452@amacapital.net>
References: <YJG6ztbGjtuctec4@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org,
        Lai Jiangshan <laijs@linux.alibaba.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andi Kleen <ak@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Uros Bizjak <ubizjak@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Juergen Gross <JGross@suse.com>,
        Joerg Roedel <jroedel@suse.de>, Jian Cai <caij2003@gmail.com>
In-Reply-To: <YJG6ztbGjtuctec4@google.com>
To:     Sean Christopherson <seanjc@google.com>
Precedence: bulk


> On May 4, 2021, at 2:21 PM, Sean Christopherson <seanjc@google.com> wrote:=

>=20
> =EF=BB=BFOn Tue, May 04, 2021, Paolo Bonzini wrote:
>>> On 04/05/21 23:05, Maxim Levitsky wrote:
>>> Does this mean that we still rely on hardware NMI masking to be activate=
d?
>>=20
>> No, the NMI code already handles reentrancy at both the assembly and C
>> levels.
>>=20
>>> Or in other words, that is we still can't have an IRET between VM exit a=
nd
>>> the entry to the NMI handler?
>>=20
>> 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 thing=
s
>> that Intel thought can be restored atomically with the VM exit.
>=20
> FWIW, NMIs are masked if the VM-Exit was due to an NMI.

Then this whole change is busted, since nothing will unmask NMIs. Revert it?=