From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4E57BC5B572 for ; Tue, 11 Aug 2026 17:51:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EEEAD6B0096; Tue, 11 Aug 2026 13:51:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EC6006B009B; Tue, 11 Aug 2026 13:51:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DDDC46B009D; Tue, 11 Aug 2026 13:51:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id AE52B6B0096 for ; Tue, 11 Aug 2026 13:51:35 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 38E421A017F for ; Tue, 11 Aug 2026 17:51:35 +0000 (UTC) X-FDA: 85089730950.13.84C3847 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf09.hostedemail.com (Postfix) with ESMTP id 781B114000C for ; Tue, 11 Aug 2026 17:51:33 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=CEtG58WZ; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786470693; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=hkUWYSo1p4I7KyJCkRY80edi6N6SRNlEyVr8qwAlIsE=; b=tTYu43P+5m59OMgeZp6CKpiSCOSXO/Vhwnc3LHtDdR4IrwjU6/kY2CTXTHaj/rhExs9fQL /fNGusWe8kvGdFFkMGSGykNkBTCc/ah9j6FcvxpTJPZlX/YaUWnvY2LD/X/9Sd9wqbf0VU nfkmooCz57JaVtd9NGJP9d1KVHk6QHM= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786470693; b=YvsXGaiV6zzn7qcwEhgYSW5Di+n+kKeTp2ysv4z3chdfrsPkYgu+FVM2xHpMYqXjpx9nEd UkY6k3a4MOoZWezKoe4uCzzknMz+SiRZLZ/K0bKWoCME8i2yLlabUiJR0T0vhfO+HuKfYg Q52q3F+zKSXET0MMJg9LLiZ1wYvhpeo= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=CEtG58WZ; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 017EF600C3; Tue, 11 Aug 2026 17:51:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A9391F000E9; Tue, 11 Aug 2026 17:51:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786470692; bh=hkUWYSo1p4I7KyJCkRY80edi6N6SRNlEyVr8qwAlIsE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=CEtG58WZP/nb7XjOILQATFtU23EQe1V5++85x1sfQItE9pg9SrqfcAdIwolUaHOdR k7nCkI9LJYVKMsmKJX6TyvhshyBr9/7aIX9RW77T3fXsjlKM9geAVDvrLNCZO1rEps c58d2fJU5s0F5yZtsKnD0HlitOMct+60SRGw6uYnadSz0nd6Gn6ujczut/UZL9v+ai ipGUdRsOTpBfE9/KApz7HXjbAh3ZmbK9Cic/hkIIrLb9aGYDPyCyPciqFkeq7UONxT t1w3zyaU0Is9AkP3G6BxapYcxBlwPgrkBymU0FhN7dpYfGz5nDK+yujgVoPxU3rxnh v9uwmxzNSdtmQ== Message-ID: Date: Tue, 11 Aug 2026 19:51:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 16/41] KVM: guest_memfd: Zero page while getting pfn To: Sean Christopherson , Ackerley Tng Cc: 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 , 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, 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: hyjjycer8hhh5ico4dkus8x7n79ahmgf X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 781B114000C X-HE-Tag: 1786470693-122120 X-HE-Meta: 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 0HLkumCC x84OiGzEykZuSTTrc6ogsrQwWE/lvplwY5eV2e1qPQ5U7C4nmxAC3NJcKqB9nQK/hq82lULhhp/xNOs1ST+aNXSvywHEmBIBBxdPyh5kSazjRFM78YiyhihAaFq7p8r6rWMzmf8BNib/25wsaIVfei/DtgAxSEAzLbnapqyQuIGez+CvqH72b4pwHCi2ildHOGNedwURHu0I+Pq4NgnozvmVkOw9tXjf5MTyWxQ7k+B0NR+WyLpgt9dX5/QAtyoir3nZ/ByPspuJI8u9tHDD4mXlUqOQ8k+QMIwFD7mBFnq3AKL06ph9gPun3IQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> Previously, without in-place conversion, populate never reads memory >> from guest_memfd so there was no danger of leaking uninitialized memory. >>> >>> In case post-populate failed, do we want to re-zero the pages? >> >> I believe we can't re-zero the pages. When SNP fails to populate it >> could be because SNP didn't like the CPUIDs userspace set up, and after >> the error userspace is expected to check what SNP likes, then >> retry. Ah, okay. >> >> IIUC zeroing will destroy the message SNP wanted to leave for userspace. >> >> Michael should be able to explain more here :) > > Not Michael, but the above is correct. If firmware rejects a CPUID page, then > KVM copies back the expected CPUID values provided by firmware. > > That said, now that we have have @may_writeback_src we _could_ re-zero the page, > i.e. only zero pages for which @may_writeback_src is %false. > > And _that_ said, I vote "no". KVM zeros the memory mostly to ensure userspace > can't read stale data, e.g. someone else's data. I don't think we need to > guarantee that a failed populate() (or rather, whatever ioctl called into it) > will leave memory in any particular state. It would be easier to document that > the page contents may be modified on failure. Let's do that then! -- Cheers, David