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b=ZWnSpcna/uvTIx6PjpZs5OMyfRL64AWMij5eBenINNuK5C0HTCn7eC7nxZskcIhjTg O5yzlKX6ZO6f1rR7MSalm3/nmARum/HdfbMqhXzU8Dyt+5HGDBOoq0+U5d1jO1O0Abdl Z47OevVNhD84SJc1bkmg3VnGSFk4QQTFy1VAPfzk8wVCxuckqaBzf2ISasLQMj3duDoW HsUglYYnHGNrKQlBhrl9TimDDKhJaL1b8c065t2/T0/ghaHu4zohX1N6ohXjYw4DvAI1 5AsgzqojvgZ19WkcBEF+T+S/tlNB5w2L9omdXTx0xzjGtQcsgU+dR1D0uwXogE/25gQC cPjQ== X-Forwarded-Encrypted: i=1; AHgh+RrPk7aQDHu1eq79UUlYutD3kOwkr6JAO1jR0rUa6JzBU8xWctL06MPkasc/kWzWeB3plvk15JGApA==@kvack.org X-Gm-Message-State: AOJu0YwPNfFMoSOAPoPLJRB74o7iw+UVIKcqiLLFQtWWJ9E+tI5u5pIL z+ZdUtYuMXumKwE4x9hd6uMhoCrcL2+koxz7qIbNG7sA8djQCxNgLbPTsf1NG539F5KnshqxkX6 0BRnLlg== X-Received: from pgcd20.prod.google.com ([2002:a05:6a02:4c54:b0:c9e:41e5:2eec]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:6a21:b0:3b5:489c:7bb5 with SMTP id adf61e73a8af0-3cc71d1e1c7mr839682637.28.1786658929498; Thu, 13 Aug 2026 15:08:49 -0700 (PDT) Date: Thu, 13 Aug 2026 15:08:48 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@google.com> <20260807-gmem-inplace-conversion-v10-12-2fc18ee6d3ba@google.com> <1ec08cd8-3072-4753-ad5e-cd34956647f8@linux.intel.com> Message-ID: Subject: Re: [PATCH v10 12/41] KVM: guest_memfd: Call arch make_shared callback for to-shared conversion From: Sean Christopherson To: Ackerley Tng Cc: Binbin Wu , aik@amd.com, andrew.jones@linux.dev, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , tarunsahu@google.com, Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, Fuad Tabba Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 331BDC0006 X-Stat-Signature: m1yhgwo77t5ydumg3ntrb1e8stwpamr7 X-HE-Tag: 1786658931-352803 X-HE-Meta: U2FsdGVkX19ty4OnCMTILPtVKip24yT/UfJSw5jEZAhKoottMY2DClA01Dh0+RwPboPiS5OpHg4LIKFslQ4FvvnYk10D3bGzDfBeIr+atQeGM5kew41ktTsBHcERDZwL+5BX3eG7lEviZe2qL+fzHqyCf/DEybQbJff9O9RaEO+nwmKJrU+VSfomP0akA68Und3w8tjkHiOL69FT7c3uJTzf5XbbRd2ZNyPr6nh+8xoDVGyCTRDSNKouSlcuV487brvexOksY8Wd8XEAw9qs15rjsdXqqeEYLWwgp1/1T+hKEQKWBDTR8akImUOtxhfK4ap3E2dmOtpVHKCgvWsrM+KPqHb+rcw9BdXzcjnqxGeuaNmRuN5F1b7mK+DtWkpZq6U8Dm/FIVWL4vBcK4BN7ZutQrbq3cx/vZiaYtW+1RnBooGr+w4VGa0NioW+nw/DAkJ+ogk+CMokSQE3/axPprGQOuxqp5vcxB+YLwUf78diUuFE+ieJyKTWzqkVZSjBVABOfbW+B/w9c8UULbWgIFgL11g0qsedBUv4xZOrGl9GmxaxGtLA9osxBv4tQxoR0cJrwCmPiRzd6L4Y8zOEKyb4pujituzz41D1iz7Us2btQeEtTbpLC3/png5ETpx0sytuFMuiALcePBa1trNSxDzd4+Xco1Mlsce3VTr8p4Duv24M3DaGbTFEDQPIto/DjqL/yL4Mo5+NVEjkIzdrbdAPW/e1lwMQSbyeEiaK8naNVQefqwj/PIjl54SqlsagbknD5MW6JekdAPDdmJ5P+7uk0gNVmxko/6IzJYKY+2z77ahVWpyvsgkojPj02Oxkn5pht8IyA7lnxG7IrvqlAPtcFmD3sCghpXhX63z5Blb7LNlT6f3HWqQMMwhLCa61fq/S/IdR2ppgQtguA3n7K8W/lkle0+iXmSqst2t2Bko2YgQ6sPmlT/7atxwGNnBLdxTNYL8r+XEKicLrP0k +PvqQ119 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 13, 2026, Ackerley Tng wrote: > Sean Christopherson writes: > > > On Thu, Aug 13, 2026, Binbin Wu wrote: > >> On 8/8/2026 5:52 AM, Ackerley Tng via B4 Relay wrote: > >> > +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT > >> > +static void kvm_gmem_make_shared(struct inode *inode, pgoff_t start, pgoff_t end) > >> > +{ > >> > + struct folio_batch fbatch; > >> > + pgoff_t next = start; > >> > + int i; > >> > + > >> > + folio_batch_init(&fbatch); > >> > + while (filemap_get_folios(inode->i_mapping, &next, end - 1, &fbatch)) { > >> > + for (i = 0; i < folio_batch_count(&fbatch); ++i) { > >> > + struct folio *folio = fbatch.folios[i]; > >> > + pgoff_t start_index, end_index; > >> > + kvm_pfn_t start_pfn; > >> > + kvm_pfn_t nr_pages; > >> > + > >> > + start_index = max(start, folio->index); > >> > + end_index = min(end, folio_next_index(folio)); > >> > + /* > >> > + * end_index is either in folio or points to > >> > + * the first page of the next folio. Hence, > >> > + * all pages in range [start_index, end_index) > >> > + * are contiguous. > >> > + */ > >> > + start_pfn = folio_file_pfn(folio, start_index); > >> > + nr_pages = end_index - start_index; > >> > + > >> > + kvm_arch_gmem_make_shared(start_pfn, nr_pages); > >> > + } > >> > + > >> > + folio_batch_release(&fbatch); > >> > + cond_resched(); > >> > + } > >> > +} > >> > +#else > >> > +static void kvm_gmem_make_shared(struct inode *inode, pgoff_t start, pgoff_t end) {} > >> > +#endif > >> > + > >> > static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start, > >> > size_t nr_pages, uint64_t attrs, > >> > pgoff_t *err_index) > >> > @@ -599,7 +636,12 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start, > >> > > >> > filter = to_private ? KVM_FILTER_SHARED : KVM_FILTER_PRIVATE; > >> > kvm_gmem_invalidate_start(inode, start, end, filter); > >> > + > >> > + if (!to_private) > > Should I make this condition > > if (!to_private && kvm_x86_ops.gmem_make_shared) > > instead? > > Will that help? No, because that's bleeding x86 details into common code, which defeats the purpose of arch hooks. That's why I think it's worth analyzing the cost: if it's in the noise, leave it alone. If it's meaningful, figure out a not-too-gross way to skip the entire thing if kvm_arch_gmem_make_shared() is a glorified nop in the end.