From: Thomas Gleixner <tglx@linutronix.de>
To: Lai Jiangshan <jiangshanlai@gmail.com>, linux-kernel@vger.kernel.org
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.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>,
kvm@vger.kernel.org, Josh Poimboeuf <jpoimboe@redhat.com>,
Uros Bizjak <ubizjak@gmail.com>,
Maxim Levitsky <mlevitsk@redhat.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>
Subject: Re: [PATCH 3/4] KVM/VMX: Invoke NMI non-IST entry instead of IST entry
Date: Mon, 03 May 2021 21:37:49 +0200 [thread overview]
Message-ID: <87k0ofk3qq.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210426230949.3561-4-jiangshanlai@gmail.com>
On Tue, Apr 27 2021 at 07:09, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com>
>
> In VMX, the NMI handler needs to be invoked after NMI VM-Exit.
>
> Before the commit 1a5488ef0dcf6 ("KVM: VMX: Invoke NMI handler via
> indirect call instead of INTn"), the work is done by INTn ("int $2").
>
> But INTn microcode is relatively expensive, so the commit reworked
> NMI VM-Exit handling to invoke the kernel handler by function call.
> And INTn doesn't set the NMI blocked flag required by the linux kernel
> NMI entry. So moving away from INTn are very reasonable.
>
> Yet some details were missed. After the said commit applied, the NMI
> entry pointer is fetched from the IDT table and called from the kernel
> stack. But the NMI entry pointer installed on the IDT table is
> asm_exc_nmi() which expects to be invoked on the IST stack by the ISA.
> And it relies on the "NMI executing" variable on the IST stack to work
> correctly. When it is unexpectedly called from the kernel stack, the
> RSP-located "NMI executing" variable is also on the kernel stack and
> is "uninitialized" and can cause the NMI entry to run in the wrong way.
>
> So we should not used the NMI entry installed on the IDT table. Rather,
> we should use the NMI entry allowed to be used on the kernel stack which
> is asm_noist_exc_nmi() which is also used for XENPV and early booting.
It's not used by XENPV. XENPV only uses the C entry point, but the ASM
entry is separate.
Thanks,
tglx
next prev parent reply other threads:[~2021-05-03 19:37 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 23:09 [PATCH 0/4] x86: Don't invoke asm_exc_nmi() on the kernel stack Lai Jiangshan
2021-04-26 23:09 ` [PATCH 1/4] x86/xen/entry: Rename xenpv_exc_nmi to noist_exc_nmi Lai Jiangshan
2021-04-28 21:27 ` Steven Rostedt
2021-04-30 7:15 ` Paolo Bonzini
2021-04-30 12:05 ` Steven Rostedt
2021-05-03 19:05 ` Thomas Gleixner
2021-05-03 19:41 ` Thomas Gleixner
2021-05-10 7:59 ` Juergen Gross
2021-04-26 23:09 ` [PATCH 3/4] KVM/VMX: Invoke NMI non-IST entry instead of IST entry Lai Jiangshan
2021-04-30 2:46 ` Lai Jiangshan
2021-05-03 19:37 ` Thomas Gleixner [this message]
2021-05-03 20:02 ` Thomas Gleixner
2021-05-04 8:10 ` Paolo Bonzini
2021-04-26 23:09 ` [PATCH 4/4] KVM/VMX: Fold handle_interrupt_nmi_irqoff() into its solo caller Lai Jiangshan
2021-04-30 9:03 ` Thomas Gleixner
2021-04-30 9:06 ` Paolo Bonzini
2021-04-30 23:28 ` Thomas Gleixner
2021-04-30 7:14 ` [PATCH 0/4] x86: Don't invoke asm_exc_nmi() on the kernel stack Paolo Bonzini
2021-05-03 14:36 ` Thomas Gleixner
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