linux-kernel - Re: [PATCH v2 1/2] KVM: x86: Check hypercall's exit to userspace generically

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Message-ID: <ZrwAGc/UPtcrN4ug@ls.amr.corp.intel.com>
Date: Tue, 13 Aug 2024 17:53:45 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: Binbin Wu <binbin.wu@...ux.intel.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, pbonzini@...hat.com,
	seanjc@...gle.com, isaku.yamahata@...el.com,
	rick.p.edgecombe@...el.com, michael.roth@....com
Subject: Re: [PATCH v2 1/2] KVM: x86: Check hypercall's exit to userspace
 generically

On Wed, Aug 14, 2024 at 11:16:44AM +1200,
"Huang, Kai" <kai.huang@...el.com> wrote:

> > ---
> >   arch/x86/kvm/x86.c | 4 ++--
> >   arch/x86/kvm/x86.h | 7 +++++++
> >   2 files changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index af6c8cf6a37a..6e16c9751af7 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -10226,8 +10226,8 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> >   	cpl = kvm_x86_call(get_cpl)(vcpu);
> >   	ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
> > -	if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
> > -		/* MAP_GPA tosses the request to the user space. */
> > +	if (!ret && is_kvm_hc_exit_enabled(vcpu->kvm, nr))
> > +		/* The hypercall is requested to exit to userspace. */
> >   		return 0;
> 
> I believe you put "!ret" check first for a reason?  Perhaps you can add a
> comment.

I think he'd like to avoid to hit WARN_ON_ONCE().
-- 
Isaku Yamahata <isaku.yamahata@...el.com>