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From: Paolo Bonzini <pbonzini@redhat.com>
To: Lai Jiangshan <jiangshanlai@gmail.com>, linux-kernel@vger.kernel.org
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	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>
Subject: Re: [PATCH 0/4] x86: Don't invoke asm_exc_nmi() on the kernel stack
Date: Fri, 30 Apr 2021 09:14:23 +0200	[thread overview]
Message-ID: <228d8b10-84cb-4dd2-8810-3c94bc3ae07b@redhat.com> (raw)
In-Reply-To: <20210426230949.3561-1-jiangshanlai@gmail.com>

On 27/04/21 01:09, 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.
> 
> During fixing the problem for KVM, I found that there might be the same
> problem for early booting stage where the IST is not set up. asm_exc_nmi()
> is not allowed to be used in this stage for the same reason about
> the RSP-located "NMI executing" variable.
> 
> For both cases, we should use asm_noist_exc_nmi() which is introduced
> in the patch 1 via renaming from an existing asm_xenpv_exc_nmi() and
> which is safe on the kernel stack.
> 
> https://lore.kernel.org/lkml/20200915191505.10355-3-sean.j.christopherson@intel.com/

For the KVM part,

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo

> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: Wanpeng Li <wanpengli@tencent.com>
> Cc: Jim Mattson <jmattson@google.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: kvm@vger.kernel.org
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Uros Bizjak <ubizjak@gmail.com>
> Cc: Maxim Levitsky <mlevitsk@redhat.com>
> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
> 
> Lai Jiangshan (4):
>    x86/xen/entry: Rename xenpv_exc_nmi to noist_exc_nmi
>    x86/entry: Use asm_noist_exc_nmi() for NMI in early booting stage
>    KVM/VMX: Invoke NMI non-IST entry instead of IST entry
>    KVM/VMX: fold handle_interrupt_nmi_irqoff() into its solo caller
> 
>   arch/x86/include/asm/idtentry.h |  4 +---
>   arch/x86/kernel/idt.c           |  8 +++++++-
>   arch/x86/kernel/nmi.c           | 12 ++++++++++++
>   arch/x86/kvm/vmx/vmx.c          | 27 ++++++++++++++-------------
>   arch/x86/xen/enlighten_pv.c     |  9 +++------
>   arch/x86/xen/xen-asm.S          |  2 +-
>   6 files changed, 38 insertions(+), 24 deletions(-)
> 


  parent reply	other threads:[~2021-04-30  7:14 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
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 ` Paolo Bonzini [this message]
2021-05-03 14:36   ` [PATCH 0/4] x86: Don't invoke asm_exc_nmi() on the kernel stack Thomas Gleixner

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