linux-kernel - Re: [PATCH v4 08/12] KVM: x86: centralize code to get CD=1 memtype when guest MTRRs are honored

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Message-ID: <ZPWLVHSbwC+CBOqP@yzhao56-desk.sh.intel.com>
Date:   Mon, 4 Sep 2023 15:46:28 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <pbonzini@...hat.com>, <chao.gao@...el.com>, <kai.huang@...el.com>,
        <robert.hoo.linux@...il.com>, <yuan.yao@...ux.intel.com>
Subject: Re: [PATCH v4 08/12] KVM: x86: centralize code to get CD=1 memtype
 when guest MTRRs are honored

On Fri, Aug 25, 2023 at 02:46:07PM -0700, Sean Christopherson wrote:
> On Fri, Jul 14, 2023, Yan Zhao wrote:
> > Centralize the code to get cache disabled memtype when guest MTRRs are
> > honored. If a TDP honors guest MTRRs, it is required to call the provided
> > API to get the memtype for CR0.CD=1.
> > 
> > This is the preparation patch for later implementation of fine-grained gfn
> > zap for CR0.CD toggles when guest MTRRs are honored.
> > 
> > No functional change intended.
> > 
> > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > ---
> >  arch/x86/kvm/mtrr.c    | 16 ++++++++++++++++
> >  arch/x86/kvm/vmx/vmx.c | 10 +++++-----
> >  arch/x86/kvm/x86.h     |  2 ++
> >  3 files changed, 23 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
> > index 3ce58734ad22..64c6daa659c8 100644
> > --- a/arch/x86/kvm/mtrr.c
> > +++ b/arch/x86/kvm/mtrr.c
> > @@ -721,3 +721,19 @@ bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
> >  
> >  	return type == mtrr_default_type(mtrr_state);
> >  }
> > +
> > +/*
> > + * this routine is supposed to be called when guest mtrrs are honored
> > + */
> > +void kvm_honors_guest_mtrrs_get_cd_memtype(struct kvm_vcpu *vcpu,
> > +					   u8 *type, bool *ipat)
> 
> I really don't like this helper.  IMO it's a big net negative for the readability
> of vmx_get_mt_mask().  As I said in the previous version, I agree that splitting
> logic is generally undesirable, but in this case I strongly believe it's the
> lesser evil.
> 
Ok, will drop this helper in the next version :)