linux-kernel - Re: [PATCH] KVM: LAPIC: Do not mask the local interrupts when LAPIC is sw disabled

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Date:   Thu, 30 May 2019 11:46:02 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org
Subject: Re: [PATCH] KVM: LAPIC: Do not mask the local interrupts when LAPIC
 is sw disabled

On Tue, May 21, 2019 at 06:44:15PM +0800, Luwei Kang wrote:
> The current code will mask all the local interrupts in the local
> vector table when the LAPIC is disabled by SVR (Spurious-Interrupt
> Vector Register) "APIC Software Enable/Disable" flag (bit8).
> This may block local interrupt be delivered to target vCPU
> even if LAPIC is enabled by set SVR (bit8 == 1) after.

The current code aligns with the SDM, which states:

  Local APIC State After It Has Been Software Disabled

  When the APIC software enable/disable flag in the spurious interrupt
  vector register has been explicitly cleared (as opposed to being cleared
  during a power up or reset), the local APIC is temporarily disabled.
  The operation and response of a local APIC while in this software-
  disabled state is as follows:

    - The mask bits for all the LVT entries are set. Attempts to reset
      these bits will be ignored.