linux-kernel - Re: [RFC PATCH v5 20/45] KVM: x86/mmu: Allocate/free S-EPT pages using tdx_{alloc,free}_control

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Message-ID: <aYJX3usu7FzPrFWa@google.com>
Date: Tue, 3 Feb 2026 12:17:34 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Kai Huang <kai.huang@...el.com>
Cc: "x86@...nel.org" <x86@...nel.org>, 
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "kas@...nel.org" <kas@...nel.org>, 
	"bp@...en8.de" <bp@...en8.de>, "mingo@...hat.com" <mingo@...hat.com>, 
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "tglx@...nel.org" <tglx@...nel.org>, 
	Rick P Edgecombe <rick.p.edgecombe@...el.com>, 
	"ackerleytng@...gle.com" <ackerleytng@...gle.com>, "sagis@...gle.com" <sagis@...gle.com>, 
	Vishal Annapurve <vannapurve@...gle.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Yan Y Zhao <yan.y.zhao@...el.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
Subject: Re: [RFC PATCH v5 20/45] KVM: x86/mmu: Allocate/free S-EPT pages
 using tdx_{alloc,free}_control_page()

On Tue, Feb 03, 2026, Kai Huang wrote:
> On Wed, 2026-01-28 at 17:14 -0800, Sean Christopherson wrote:
> >  	int (*set_external_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level,
> >  				 u64 mirror_spte);
> > -
> > -	/* Update external page tables for page table about to be freed. */
> >  	void (*reclaim_external_sp)(struct kvm *kvm, gfn_t gfn,
> >  				    struct kvm_mmu_page *sp);
> > -
> > -	/* Update external page table from spte getting removed, and flush TLB. */
> 
> The above two comments are still useful to me.
> 
> Not sure why do you want to remove them, especially in _this_ patch?

My intent was to replace the individual comments with a more generic comment for
all of the "external" hooks.  For things like "and flush TLB", IMO those comments
belong at the call sites, not at this point.  E.g. _KVM_ doesn't require a TLB
flush in all cases.  And so for the definition of the hooks, I would prefer a more
generic comment, so that if there are details that matter to the usage, they are
documented there.

> >  	void (*remove_external_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level,
> >  				     u64 mirror_spte);
> >  
> > +
> 
> Unintentional change?

Ya.

> 
> >  	bool (*has_wbinvd_exit)(void);
> >  
> >  	u64 (*get_l2_tsc_offset)(struct kvm_vcpu *vcpu);
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 3911ac9bddfd..9b5a6861e2a4 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -6690,11 +6690,13 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
> >  	vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
> >  	vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
> >  
> > -	vcpu->arch.mmu_shadow_page_cache.init_value =
> > -		SHADOW_NONPRESENT_VALUE;
> > +	vcpu->arch.mmu_shadow_page_cache.init_value = SHADOW_NONPRESENT_VALUE;
> >  	if (!vcpu->arch.mmu_shadow_page_cache.init_value)
> >  		vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
> 
> Ditto.  Not sure this adjustment is intentional?

Heh, I'm pretty sure it was intentional, but yeah, doesn't belong here.