linux-kernel - Re: [PATCH v6 01/16] KVM: TDP_MMU: Go to next level if smaller private mapping exists

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Date:   Thu, 16 Nov 2023 17:05:21 -0800
From:   Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
        hang.yuan@...el.com, tina.zhang@...el.com,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v6 01/16] KVM: TDP_MMU: Go to next level if smaller
 private mapping exists

On Thu, Nov 16, 2023 at 09:32:22AM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 11/7/2023 11:00 PM, isaku.yamahata@...el.com wrote:
> > From: Xiaoyao Li <xiaoyao.li@...el.com>
> > 
> > Cannot map a private page as large page if any smaller mapping exists.
> > 
> > It has to wait for all the not-mapped smaller page to be mapped and
> > promote it to larger mapping.
> > 
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> > ---
> >   arch/x86/kvm/mmu/tdp_mmu.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 2c5257628881..d806574f7f2d 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -1287,7 +1287,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >   	tdp_mmu_for_each_pte(iter, mmu, is_private, raw_gfn, raw_gfn + 1) {
> >   		int r;
> > -		if (fault->nx_huge_page_workaround_enabled)
> > +		if (fault->nx_huge_page_workaround_enabled ||
> > +		    kvm_gfn_shared_mask(vcpu->kvm))
> As I mentioned in https://lore.kernel.org/kvm/fef75d54-e319-5170-5f76-f5abc4856315@linux.intel.com/,
> The change of this patch will not take effect.
> If "fault->nx_huge_page_workaround_enabled" is false, the condition
> "spte_to_child_sp(spte)->nx_huge_page_disallowed" will not be true.
> 
> IIUC, the function disallowed_hugepage_adjust() currently is only to handle
> nx_huge_page_workaround, it seems no special handling needed for TD.
> >   			disallowed_hugepage_adjust(fault, iter.old_spte, iter.level);
> >   		/*

You're correct. Now guest memfd memory attributes takes care of large page
mapping, this patch is uncessary.  Will drop this patch.
-- 
Isaku Yamahata <isaku.yamahata@...ux.intel.com>