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Fri, 23 Oct 2026 01:21:58 +0000 Date: Fri, 23 Oct 2026 09:20:59 +0800 From: Yan Zhao To: "Edgecombe, Rick P" , "Du, Fan" , "kvm@vger.kernel.org" , "Li, Xiaoyao" , "Hansen, Dave" , "thomas.lendacky@amd.com" , "vbabka@suse.cz" , "tabba@google.com" , "david@kernel.org" , "kas@kernel.org" , "binbin.wu@linux.intel.com" , "seanjc@google.com" , "pbonzini@redhat.com" , "Peng, Chao P" , "ackerleytng@google.com" , "michael.roth@amd.com" , "nik.borisov@suse.com" , "linux-kernel@vger.kernel.org" , "sagis@google.com" , "Annapurve, Vishal" , "Chen, Farrah" , "Gao, Chao" , "francescolavra.fl@gmail.com" , "Miao, Jun" , "jgross@suse.com" , "pgonda@google.com" , "x86@kernel.org" Subject: Re: [PATCH v4 08/17] KVM: TDX: Adjust the topup count of DPAMT page pairs for splitting S-EPT Message-ID: Reply-To: Yan Zhao References: <71682b712350b5270e4a0f5cddceb1da12341b9d.camel@intel.com> <25927de50b85816956e8989f402ff6ccfa8fa0ba.camel@intel.com> <55ccf641218c6553b2f43f4394b92c23bd8b5d98.camel@intel.com> Content-Type: text/plain; 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> > >         int dpamt_pairs = min_nr_spts; > > > > > >         pamt_cache = tdx_get_pamt_cache(kvm, vcpu); > > >         if (!pamt_cache) if (KVM_BUG_ON(!pamt_cache, kvm)) If no objection, I'll add KVM_BUG_ON() here to avoid unnecessary repeated retries of topup() after such an error occurs, as it would indicate a KVM bug. > > >                 return -EIO; > > > > > >         /* DPAMT page pair for the root SPT has already been installed */ > > >         if (with_root_spt) > > >                 dpamt_pairs -= 1; > > > > > >         /* +1 pair for 4KB guest private page */ > > >         dpamt_pairs += 1; > > > > > >         return tdx_topup_pamt_cache(pamt_cache, dpamt_pairs); > > > } > > > > Yes this looks much clearer than even the upstream code. Do you have any better > > ideas than "4KB guest private page" though? Because in the split case it is > > actually for 512 guest private pages. We should put an artful comment to explain > > both cases while not making it look like something that has a better solution. > > Because I'm thinking there isn't one. > > What about a comment like > /* > * +1 pair to account for mapping a new 4KB guest page or splitting a > * 2MB guest page into 512 4KB pages. > */ > ? > > > > In the fault path, mmu_topup_memory_caches() calls: > > > r = kvm_x86_call(topup_external_cache)(vcpu->kvm, vcpu, true, > > > PT64_ROOT_MAX_LEVEL); > > > > > > In the split path, tdp_mmu_alloc_sp_for_split() calls: > > > kvm_x86_call(topup_external_cache)(kvm, kvm_get_running_vcpu(), false, 1); > >