Re: [PATCHv2 08/12] KVM: TDX: Handle PAMT allocation in fault path

[Edgecombe, Rick P]

On Thu, 2025-08-21 at 14:21 -0500, Sagi Shahar wrote:
> >   int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
> >                                enum pg_level level, kvm_pfn_t pfn)
> >   {
> > +       struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
> >          struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> >          struct page *page = pfn_to_page(pfn);
> > +       int ret;
> > +
> > +       ret = tdx_pamt_get(page, level, tdx_alloc_pamt_page_atomic, vcpu);
> > +       if (ret)
> > +               return ret;
> 
> tdx_pamt_get() can return non-zero value in case of success e.g.
> returning 1 in case tdx_pamt_add() lost the race. 

No?

+static int tdx_pamt_get(struct page *page, enum pg_level level)
+{
+	unsigned long hpa = page_to_phys(page);
+	atomic_t *pamt_refcount;
+	LIST_HEAD(pamt_pages);
+	int ret;
+
+	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
+		return 0;
+
+	if (level != PG_LEVEL_4K)
+		return 0;
+
+	pamt_refcount = tdx_get_pamt_refcount(hpa);
+	WARN_ON_ONCE(atomic_read(pamt_refcount) < 0);
+
+	if (atomic_inc_not_zero(pamt_refcount))
+		return 0;
+
+	if (tdx_alloc_pamt_pages(&pamt_pages))
+		return -ENOMEM;
+
+	ret = tdx_pamt_add(pamt_refcount, hpa, &pamt_pages);
+	if (ret)
+		tdx_free_pamt_pages(&pamt_pages);
+
+	return ret >= 0 ? 0 : ret;
+}

> Shouldn't we check
> for (ret < 0) here and below cases?

I think you are thinking of tdx_pamt_add().