linux-kernel - Re: [PATCH v19 010/130] KVM: x86: Pass is_private to gmem hook of gmem_max

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Date: Fri, 19 Apr 2024 11:28:48 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Yan Zhao <yan.y.zhao@...el.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>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 010/130] KVM: x86: Pass is_private to gmem hook of
 gmem_max_level

On Fri, Apr 19, 2024 at 09:19:29AM +0800,
Yan Zhao <yan.y.zhao@...el.com> wrote:

> On Mon, Feb 26, 2024 at 12:25:12AM -0800, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > TDX wants to know the faulting address is shared or private so that the max
> > level is limited by Secure-EPT or not.  Because fault->gfn doesn't include
> > shared bit, gfn doesn't tell if the faulting address is shared or not.
> > Pass is_private for TDX case.
> > 
> > TDX logic will be if (!is_private) return 0; else return PG_LEVEL_4K.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h | 3 ++-
> >  arch/x86/kvm/mmu/mmu.c          | 3 ++-
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index d15f5b4b1656..57ce89fc2740 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1797,7 +1797,8 @@ struct kvm_x86_ops {
> >  
> >  	gva_t (*get_untagged_addr)(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags);
> >  
> > -	int (*gmem_max_level)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, u8 *max_level);
> > +	int (*gmem_max_level)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn,
> > +			      bool is_private, u8 *max_level);
> >  };
> >  
> >  struct kvm_x86_nested_ops {
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 1e5e12d2707d..22db1a9f528a 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4324,7 +4324,8 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> >  
> >  	max_level = kvm_max_level_for_order(max_order);
> >  	r = static_call(kvm_x86_gmem_max_level)(vcpu->kvm, fault->pfn,
> > -						fault->gfn, &max_level);
> > +						fault->gfn, fault->is_private,
> > +						&max_level);
> fault->is_private is always true in kvm_faultin_pfn_private().
> Besides, as shared page allocation will not go to kvm_faultin_pfn_private(),
> why do we need to add the "is_private" parameter ?

You're right, we don't need this patch.
As Paolo picked the patch to add a hook, the discussion is happening at
https://lore.kernel.org/all/20240409234632.fb5mly7mkgvzbtqo@amd.com/#t
-- 
Isaku Yamahata <isaku.yamahata@...el.com>