From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9B2D13B0AFA; Mon, 10 Aug 2026 09:30:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786354252; cv=none; b=cEsppQ2dK0b/TGhAILdpr2Qlg0AAV4aEiIduj3XUVBJq/yqWPRzjceKClUWI2XZ1DN4gCOr4+zU71u8PvdQ64u0olWh7V0NGFKhG9SDpcojUp6m8IsElqfyRmdd0KaCeGN8cN+UbAxNLfHUwPv9S+KOyCOX3bEQ5Tv7M7twyJAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786354252; c=relaxed/simple; bh=CforaZHhCp0D4PRuKp5wg559Zx2JmhiPGocYgW6LoZs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=b43eeqapUz3tDnxyOVQb0TyuUo6vZdylRWeWfzgfi51XOVdiZjXgTfP9Gpjfv5k4fgooD0kMYmDa2MRolA7cvksd/q9fkk4s2+WRm94MUptoHkGfdNdBvC1d8YheGKwEwb7eplv5S3ff/sHSB85CsiU6G3HlnL0ewZcUEse15zU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bohlnxP3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bohlnxP3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E10BE1F000E9; Mon, 10 Aug 2026 09:30:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786354250; bh=l2my6VqSN1Pi6OPxK0/5FmAellJIX3EJ4Czc065zjm4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bohlnxP3jBpV1WhsLd9bskHbEHKnYQzLSBniquP2TI1eoX9xUZkhF6o4QCGeexn9I eIcYh4ZZt9g5AoC91V4GVEDjgaiFPnNwuUPdyYGwgYOXOy25mXQv2j60thszqnLr8T ecFbv0GHwaNwhLeQstEov/iTQWIdVq2h8eDuKRc4TlNUmKk2INXLZIZy0HB+1F3JWA xzmccK5095T+EepC03FnWQCvmvzYl/VqbOakMLBMAuLFYP61issA2uA8g7TuNQoh1O oXJl7l3BW5Eb4kwXsPNYzzBpHdF/RtbsGptzlyJ1kBQGQSEe493MF8azC9K8Nyt5in svnE5Oj2krolQ== Message-ID: Date: Mon, 10 Aug 2026 11:30:29 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 16/41] KVM: guest_memfd: Zero page while getting pfn To: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, 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 , Sean Christopherson , 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 Cc: 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, Xiaoyao Li References: <20260807-gmem-inplace-conversion-v10-0-2fc18ee6d3ba@google.com> <20260807-gmem-inplace-conversion-v10-16-2fc18ee6d3ba@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260807-gmem-inplace-conversion-v10-16-2fc18ee6d3ba@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/7/26 23:52, Ackerley Tng via B4 Relay wrote: > From: Ackerley Tng > > Move the folio initialization logic from kvm_gmem_get_pfn() into > __kvm_gmem_get_pfn() to also zero pages if the page is to be used in > kvm_gmem_populate(). > > With in-place conversion, the existing data in a guest_memfd page can be > populated into guest memory through platform-specific ioctls. > > Without first zeroing the page obtained using __kvm_gmem_get_pfn(), it > might contain uninitialized host memory, which would leak to the guest if > the populate completes. > > guest_memfd pages are zeroed at most once in the page's entire lifetime > with guest_memfd, and that is tracked using the uptodate flag. > > Zeroing the page in __kvm_gmem_get_pfn() is chosen over zeroing in > kvm_gmem_get_folio() since other flows, such as a future write() syscall, > can get a page, write to the page and then set page uptodate without > zeroing. > > This aligns with the concept of zeroing before first use - the other place > where zeroing happens is in kvm_gmem_fault_user_mapping(). > > Don't mark the page uptodate again after populating, since the page would > already be marked uptodate before the post_populate() call. The downside is that __kvm_gmem_populate() will now zero+write. I assume we don't care about possible performance impacts? Worth spelling that out. > > Reviewed-by: Fuad Tabba > Tested-by: Shivank Garg > Reviewed-by: Xiaoyao Li > Signed-off-by: Ackerley Tng > --- > virt/kvm/guest_memfd.c | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 030af0855f8b0..41950c8105b5d 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -1079,6 +1079,11 @@ static struct folio *__kvm_gmem_get_pfn(struct file *file, > return ERR_PTR(-EHWPOISON); > } > > + if (!folio_test_uptodate(folio)) { > + clear_highpage(folio_page(folio, 0)); > + folio_mark_uptodate(folio); > + } > + > *pfn = folio_file_pfn(folio, index); > if (max_order) > *max_order = 0; > @@ -1108,11 +1113,6 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, > goto out; > } > > - if (!folio_test_uptodate(folio)) { > - clear_highpage(folio_page(folio, 0)); > - folio_mark_uptodate(folio); > - } > - > #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT > if (kvm_gmem_is_private_mem(file_inode(file), index)) > r = kvm_arch_gmem_make_private(kvm, gfn, *pfn, > @@ -1159,8 +1159,6 @@ static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, > } > > ret = post_populate(kvm, gfn, pfn, src_page, opaque); > - if (!ret) > - folio_mark_uptodate(folio); In case post-populate failed, do we want to re-zero the pages? -- Cheers, David