Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 20 Jul 2022 17:18:19 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Chao Gao <chao.gao@intel.com>
Cc:     Kechen Lu <kechenl@nvidia.com>, kvm@vger.kernel.org,
        pbonzini@redhat.com, vkuznets@redhat.com, somduttar@nvidia.com,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v3 4/7] KVM: x86: Let userspace re-enable previously
 disabled exits
Message-ID: <Ytg428sleo7uMRQt@google.com>
References: <20220615011622.136646-1-kechenl@nvidia.com>
 <20220615011622.136646-5-kechenl@nvidia.com>
 <20220615025114.GB7808@gao-cwp>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220615025114.GB7808@gao-cwp>
Precedence: bulk

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.