linux-kernel - Re: [PATCH 2/2] KVM: x86: Fix split-irqchip vs interrupt injection window request

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Message-ID: <4a9e11b1-9cd6-b9a4-d9ea-f2f4d0983084@redhat.com>
Date:   Tue, 13 Apr 2021 14:10:02 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Filippo Sironi <sironi@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "v4.7+" <stable@...r.kernel.org>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 2/2] KVM: x86: Fix split-irqchip vs interrupt injection
 window request

On 12/04/21 23:43, Sean Christopherson wrote:
> where kvm_arch_interrupt_allowed() checks EFLAGS.IF (and an edge case related to
> nested virtualization).  KVM also captures EFLAGS.IF in vcpu->run->if_flag.
> For whatever reason, QEMU checks both vcpu->run flags before injecting an IRQ,
> maybe to handle a case where QEMU itself clears EFLAGS.IF?

It's mostly obsolete code (that will be deprecated in the next version 
and removed in about a year) so I wouldn't read much into it.  if_flag 
itself is obsolete; it is not provided by SEV-ES, and a useless subset 
of ready_for_interrupt_injection.

Paolo