linux-kernel - Re: [RFC PATCH v2 22/23] KVM: TDX: Handle Dynamic PAMT on page split

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Message-ID: <CAGtprH8da6iwwG6u6Z2EpGaqFVWWFJD4o3RUvDYmxDQ9qaYm0w@mail.gmail.com>
Date: Thu, 14 Aug 2025 11:29:54 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: pbonzini@...hat.com, seanjc@...gle.com, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, x86@...nel.org, rick.p.edgecombe@...el.com, 
	dave.hansen@...el.com, kas@...nel.org, tabba@...gle.com, 
	ackerleytng@...gle.com, quic_eberman@...cinc.com, michael.roth@....com, 
	david@...hat.com, vbabka@...e.cz, thomas.lendacky@....com, pgonda@...gle.com, 
	zhiquan1.li@...el.com, fan.du@...el.com, jun.miao@...el.com, 
	ira.weiny@...el.com, isaku.yamahata@...el.com, xiaoyao.li@...el.com, 
	binbin.wu@...ux.intel.com, chao.p.peng@...el.com
Subject: Re: [RFC PATCH v2 22/23] KVM: TDX: Handle Dynamic PAMT on page split

On Wed, Aug 13, 2025 at 10:31 PM Vishal Annapurve <vannapurve@...gle.com> wrote:
>
> On Thu, Aug 7, 2025 at 2:46 AM Yan Zhao <yan.y.zhao@...el.com> wrote:
> >
> > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > +static struct page *tdx_alloc_pamt_page_split(void *data)
> > +{
> > +       struct kvm *kvm = data;
> > +       void *p;
> > +
> > +       p = kvm_mmu_memory_cache_alloc(&kvm->arch.pamt_page_cache);
> > +       return virt_to_page(p);
> > +}
> > +
> >  static int tdx_spte_demote_private_spte(struct kvm *kvm, gfn_t gfn,
> > -                                       enum pg_level level, struct page *page)
> > +                                       enum pg_level level, struct page *page,
> > +                                       kvm_pfn_t pfn_for_gfn)
> >  {
> >         int tdx_level = pg_level_to_tdx_sept_level(level);
> > +       hpa_t hpa = pfn_to_hpa(pfn_for_gfn);
> >         struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> >         gpa_t gpa = gfn_to_gpa(gfn);
> >         u64 err, entry, level_state;
> > +       LIST_HEAD(pamt_pages);
> > +
> > +       tdx_pamt_get(page, PG_LEVEL_4K, tdx_alloc_pamt_page_split, kvm);
>
> This invocation needs a return value check.
>
> > +       tdx_alloc_pamt_pages(&pamt_pages, tdx_alloc_pamt_page_split, kvm);
>
> IIUC tdx_pamt_get() will result in pamt_pages allocation above, so
> this step is not needed.

I missed that one allocation is to cover the EPT page and another is
for HPA ranges backing the GPA mappings. So ignore my rest of the
comments except about the error handling for tdx_pamt_get() and
tdx_alloc_pamt_pages() missing in this patch.