linux-kernel - Re: [RFC PATCH v3 4/7] KVM: x86: Let userspace re-enable previously disabled exits

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Message-ID: <Ytg428sleo7uMRQt@google.com>
Date:   Wed, 20 Jul 2022 17:18:19 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     Kechen Lu <kechenl@...dia.com>, kvm@...r.kernel.org,
        pbonzini@...hat.com, vkuznets@...hat.com, somduttar@...dia.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 4/7] KVM: x86: Let userspace re-enable previously
 disabled exits

On Wed, Jun 15, 2022, Chao Gao wrote:
> On Tue, Jun 14, 2022 at 06:16:19PM -0700, Kechen Lu wrote:
> > 7.14 KVM_CAP_S390_HPAGE_1M
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index f31ebbb1b94f..7cc8ac550bc7 100644
> >--- a/arch/x86/kvm/x86.c
> >+++ b/arch/x86/kvm/x86.c
> >@@ -4201,11 +4201,10 @@ static inline bool kvm_can_mwait_in_guest(void)
> > 
> > static u64 kvm_get_allowed_disable_exits(void)
> > {
> >-	u64 r = KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
> >-		KVM_X86_DISABLE_EXITS_CSTATE;
> >+	u64 r = KVM_X86_DISABLE_VALID_EXITS;
> > 
> >-	if(kvm_can_mwait_in_guest())
> >-		r |= KVM_X86_DISABLE_EXITS_MWAIT;
> >+	if (!kvm_can_mwait_in_guest())
> >+		r &= ~KVM_X86_DISABLE_EXITS_MWAIT;
> 
> This hunk looks like a fix to patch 3; it can be squashed into that patch.

It's not a fix, just an inversion of the logic to make it easier to maintain
going forward.  I intentionally made the change in patch 4 so that adding the
kvm_get_allowed_disable_exits() is a more "pure" movement of code from the "check"
path to a common helper.

I agree it's kinda odd, but I still think splitting the changes is desirable.