linux-kernel - Re: [RFC PATCH v5 22/45] KVM: TDX: Get/put PAMT pages when (un)mapping private memory

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Message-ID: <aYYQ7Vx95ZrsqwCv@google.com>
Date: Fri, 6 Feb 2026 08:03:57 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: Thomas Gleixner <tglx@...nel.org>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Kiryl Shutsemau <kas@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, 
	linux-coco@...ts.linux.dev, kvm@...r.kernel.org, 
	Kai Huang <kai.huang@...el.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Vishal Annapurve <vannapurve@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>, 
	Sagi Shahar <sagis@...gle.com>, Binbin Wu <binbin.wu@...ux.intel.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [RFC PATCH v5 22/45] KVM: TDX: Get/put PAMT pages when
 (un)mapping private memory

On Fri, Feb 06, 2026, Yan Zhao wrote:
> On Wed, Jan 28, 2026 at 05:14:54PM -0800, Sean Christopherson wrote:
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 6e84dbc89e79..a6e4ab76b1b2 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1863,6 +1863,7 @@ struct kvm_x86_ops {
> >  				    struct kvm_mmu_page *sp);
> >  	void (*remove_external_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level level,
> >  				     u64 mirror_spte);
> > +	int (*topup_external_cache)(struct kvm_vcpu *vcpu, int min);
> >  
> >  
> >  	bool (*has_wbinvd_exit)(void);
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 9b5a6861e2a4..4ecbf216d96f 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -605,6 +605,10 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
> >  					       PT64_ROOT_MAX_LEVEL);
> >  		if (r)
> >  			return r;
> > +
> > +		r = kvm_x86_call(topup_external_cache)(vcpu, PT64_ROOT_MAX_LEVEL);
> If this external cache is for PAMT pages allocation for guest pages only, here
> the min count should be 1 instead of PT64_ROOT_MAX_LEVEL?

Oh!  Right.  Hmm, with that in mind, it seems like topup_external_cache() isn't
quite the right interace.  It's not at all clear that, unlike the other caches,
the DPAMT cache isn't tied to the page tables, it's tied to the physical memory
being mapped into the guest.

At the very least, it seems like we should drop the @min parameter?

	int (*topup_external_cache)(struct kvm *kvm, struct kvm_vcpu *vcpu);

Though if someone has a name that better captures what the cache is used for,
without bleeding too many details into common x86...