From: Steven Rostedt <rostedt@goodmis.org>
To: Lai Jiangshan <jiangshanlai+lkml@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Uros Bizjak <ubizjak@gmail.com>, Andi Kleen <ak@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Sean Christopherson <seanjc@google.com>,
Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH v2 2/2] KVM: VMX: Invoke NMI handler via indirect call instead of INTn
Date: Mon, 26 Apr 2021 21:00:20 -0400 [thread overview]
Message-ID: <20210426210020.417e3cfc@oasis.local.home> (raw)
In-Reply-To: <CAJhGHyDrAwKO1iht=d0j+OKD1U7e1fzLminudxo2sPHbF53TKQ@mail.gmail.com>
On Tue, 27 Apr 2021 08:54:37 +0800
Lai Jiangshan <jiangshanlai+lkml@gmail.com> wrote:
> > However, I'm not sure which of the two situations is better: entering
> > the NMI handler on the IST without setting the hidden NMI-blocked flag
> > could be a recipe for bad things as well.
>
> The change makes the ASM NMI entry called on the kernel stack. But the
> ASM NMI entry expects it on the IST stack and it plays with "NMI executing"
> variable on the IST stack. In this change, the stranded ASM NMI entry
> will use the wrong/garbage "NMI executing" variable on the kernel stack
> and may do some very wrong thing.
I missed this detail.
>
> Sorry, in my reply, "the NMI handler" meant to be the ASM entry installed
> on the IDT table which really expects to be NMI-masked at the beginning.
>
> The C NMI handler can handle the case of nested NMIs, which is useful
> here. I think we should change it to call the C NMI handler directly
> here as Andy Lutomirski suggested:
Yes, because that's the way x86_32 works.
>
> On Mon, Apr 26, 2021 at 11:09 PM Andy Lutomirski <luto@amacapital.net> wrote:
> > The C NMI code has its own reentrancy protection and has for years.
> > It should work fine for this use case.
>
> I think this is the right way.
Agreed.
-- Steve
next prev parent reply other threads:[~2021-04-27 1:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 19:15 [PATCH v2 0/2] KVM: VMX: Clean up IRQ/NMI handling Sean Christopherson
2020-09-15 19:15 ` [PATCH v2 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine Sean Christopherson
2020-09-15 19:27 ` Josh Poimboeuf
2020-09-15 19:38 ` Uros Bizjak
2020-09-15 19:15 ` [PATCH v2 2/2] KVM: VMX: Invoke NMI handler via indirect call instead of INTn Sean Christopherson
2021-04-26 9:33 ` Lai Jiangshan
2021-04-26 10:40 ` Paolo Bonzini
2021-04-26 11:44 ` Maxim Levitsky
2021-04-26 13:59 ` Steven Rostedt
2021-04-26 14:51 ` Andi Kleen
2021-04-26 15:09 ` Andy Lutomirski
2021-04-27 0:54 ` Lai Jiangshan
2021-04-27 1:00 ` Steven Rostedt [this message]
2021-04-27 7:05 ` Paolo Bonzini
2021-04-30 2:56 ` Lai Jiangshan
2020-09-22 13:38 ` [PATCH v2 0/2] KVM: VMX: Clean up IRQ/NMI handling Paolo Bonzini
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