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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EE8BC02182 for ; Thu, 23 Jan 2025 14:21:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 243FC280002; Thu, 23 Jan 2025 09:21:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1CBFB280001; Thu, 23 Jan 2025 09:21:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 04537280002; Thu, 23 Jan 2025 09:21:18 -0500 (EST) 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 CEA3E280001 for ; Thu, 23 Jan 2025 09:21:18 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 6D6B04923B for ; Thu, 23 Jan 2025 14:21:18 +0000 (UTC) X-FDA: 83038929036.19.A3D4B62 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf24.hostedemail.com (Postfix) with ESMTP id C4737180016 for ; Thu, 23 Jan 2025 14:21:15 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YhcYexup; spf=pass (imf24.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1737642076; 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=5MrmQK9w/1z5lvjGW1AtjnA4JrdWWyhd7SksuBzXv5g=; b=H04dx3wObYRJehh/tl2vO84604fuVhGODyBxnva8z/DtTUzMX729U5cUydOuSOvPgbiIMY nYRbkZ8y4DpZaYUb4FhcuMccY+YrwK1cYTb40jYl9VWxij5QNdfstiga3A+SR77smDQBS3 mSqhV7/r2wpfl7M8GrISxj3uIniPnOA= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=YhcYexup; spf=pass (imf24.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1737642076; a=rsa-sha256; cv=none; b=uZvWlGpsBBIM0ath/KTKrK5/OVhbwh+r8QpqNbk3WQHWu+Kqcux8OXzuYirIIbNPfdSsNV 7YL7DpH6IoEZD+FuQX3LIzNo+O+0lQIbLtKIN3UgcgPYlSmFUVZp4VUzGiL4YVzJCKsemy cABZvys8SzmnsgYUrnvbrASA00OHN9A= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1737642075; h=from:from: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:autocrypt:autocrypt; bh=5MrmQK9w/1z5lvjGW1AtjnA4JrdWWyhd7SksuBzXv5g=; b=YhcYexupsQRNCrJbU456SD5lhXd6YDT4a6pgHpn1Ed5y1cFU6FyAT92eYNsRTES2+4gfGG Q5A/Rlz9IXkgD0/qqAqEguonzOM65LeAZaqHCE0F+whWgITMusvjBmBN0GSdaxlVwhOtWt YbFJJalCyXY6ynO0mBbZKm0fd33XwSY= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-299-R7lSMD4BNa--VrvU7nrlHw-1; Thu, 23 Jan 2025 09:21:13 -0500 X-MC-Unique: R7lSMD4BNa--VrvU7nrlHw-1 X-Mimecast-MFC-AGG-ID: R7lSMD4BNa--VrvU7nrlHw Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-43624b08181so5351605e9.0 for ; Thu, 23 Jan 2025 06:21:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1737642072; x=1738246872; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=5MrmQK9w/1z5lvjGW1AtjnA4JrdWWyhd7SksuBzXv5g=; b=UBD16rw2x7kkQWH43mkn50fffidgO4Sd3Ur/Id6a9jZmCzR3Xc1dVTqSybHU0Fcxo/ YoZoHg7x4M+xy5QNLGCKsGvs1XfdGH6W4Qj2kWNXdAd38FqM4jelQuON0mBLrSoiefEe mtcvnujIhB7O5kyTJdScv7fv1L1LEaSWPqJ4UTgehLVdlWTjrBQL6kNPT1t70eZxAQGF Sj/4/hrLepA5xe0aA2J0IXOB4RlgyZafCb2WxW3w92VeriuTRjhDWfVAg8d9oEqiZPxP 5HkixyjYeg2Z7Pb5YylejvzQz5E3QU/zJsv7taGeDvIq9g4uXHnCqKKCF6IcHzwZJzyp O5/Q== X-Forwarded-Encrypted: i=1; AJvYcCX99kCsJfxgFP1G0eNC1hXMB4BCdQCI471lj++SAjyKJGJnEfJ3P1HcyA67WMV9LcVDPduTSYz4sA==@kvack.org X-Gm-Message-State: AOJu0Yw8fr1mJoTtScnuCb07UwdOWCcexEtMWOBMZidcq+Pp9t6YeajS PWibQm+6GCPp3R/vfyphqEG3+IvMFx7zg2G9jQVexbIxnpvEWMWPzKId9ynaAcY/W+YWhHH5ImZ MPi/m8ltt7u8Lm2bVhrRGHLx88SimxoJRr7N9AQY0YMo5dJcG X-Gm-Gg: ASbGnctt2Z2DSGeBogi4HFvnh8zzs/OfNs2drFJHYsvE0lkx8oFOKMrxvoN3kEUYsqc Fs2ewBJdnS3Hr1byGiiM7CBvaVX3kghyhhLdmXOmz6GbYDtmsT/4BGKPYHuOz424gOnG4yEpyJo +iihnmG6NXCyfsHwPAzVgq8OliF0WIDJX5YT8NdETJTkzT6fQLsp/iUUAYomSIXN+uXhCE7zr57 6iyawc4a0D+NhobB2/F93R6jg+XaUbrJg8ruoImHx/77G1wgfTeNmB3R7ZG8T5FMD4cE2k5EFyT +ZOVCQg9/gSj6CpqOY4DVxiZByBrQXnrsjnweLC66imIfnG3ClcicT5UZ6Ok1xFQzEfmgUS6Zkq Zp85k/OZkhIdAa9lgrzVB5w== X-Received: by 2002:a05:600c:3ba9:b0:434:e892:1033 with SMTP id 5b1f17b1804b1-438b883eccfmr34069405e9.2.1737642071911; Thu, 23 Jan 2025 06:21:11 -0800 (PST) X-Google-Smtp-Source: AGHT+IHzA/kVcfU1Nvmt+fPOYVsEAXLug0LaBWZ86dBgJXTmu4qHIOWDkHqTONVlCbE7dTT/KD8Z9g== X-Received: by 2002:a05:600c:3ba9:b0:434:e892:1033 with SMTP id 5b1f17b1804b1-438b883eccfmr34068805e9.2.1737642071390; Thu, 23 Jan 2025 06:21:11 -0800 (PST) Received: from ?IPV6:2003:cb:c70b:b400:e20a:6d03:7ac8:f97d? (p200300cbc70bb400e20a6d037ac8f97d.dip0.t-ipconnect.de. [2003:cb:c70b:b400:e20a:6d03:7ac8:f97d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438b31adbccsm66208405e9.19.2025.01.23.06.21.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2025 06:21:10 -0800 (PST) Message-ID: <164e9d74-2f1f-4557-afda-06712e8415b0@redhat.com> Date: Thu, 23 Jan 2025 15:21:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 2/9] KVM: guest_memfd: Add guest_memfd support to kvm_(read|/write)_guest_page() To: Patrick Roy , Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com References: <20250122152738.1173160-1-tabba@google.com> <20250122152738.1173160-3-tabba@google.com> <82d8d3a3-6f06-4904-9d94-6f92bba89dbc@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: C0gauLDC2tzR8T6EsiaNeCkTtzU0o1HDf-ZCNnLpuDA_1737642072 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C4737180016 X-Stat-Signature: aiftzmadqtx5z6drwpcqnb8nhgaaai7i X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1737642075-261576 X-HE-Meta: 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 kZ1Mlea0 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 23.01.25 14:57, Patrick Roy wrote: > > > On Thu, 2025-01-23 at 12:28 +0000, Fuad Tabba wrote: >> Hi Patrick, >> >> On Thu, 23 Jan 2025 at 11:57, Patrick Roy wrote: >>> >>> >>> >>> On Thu, 2025-01-23 at 11:39 +0000, David Hildenbrand wrote: >>>> On 23.01.25 10:48, Fuad Tabba wrote: >>>>> On Wed, 22 Jan 2025 at 22:10, David Hildenbrand wrote: >>>>>> >>>>>> On 22.01.25 16:27, Fuad Tabba wrote: >>>>>>> Make kvm_(read|/write)_guest_page() capable of accessing guest >>>>>>> memory for slots that don't have a userspace address, but only if >>>>>>> the memory is mappable, which also indicates that it is >>>>>>> accessible by the host. >>>>>> >>>>>> Interesting. So far my assumption was that, for shared memory, user >>>>>> space would simply mmap() guest_memdd and pass it as userspace address >>>>>> to the same memslot that has this guest_memfd for private memory. >>>>>> >>>>>> Wouldn't that be easier in the first shot? (IOW, not require this patch >>>>>> with the cost of faulting the shared page into the page table on access) >>>>> >>>> >>>> In light of: >>>> >>>> https://lkml.kernel.org/r/20250117190938.93793-4-imbrenda@linux.ibm.com >>>> >>>> there can, in theory, be memslots that start at address 0 and have a >>>> "valid" mapping. This case is done from the kernel (and on special s390x >>>> hardware), though, so it does not apply here at all so far. >>>> >>>> In practice, getting address 0 as a valid address is unlikely, because >>>> the default: >>>> >>>> $ sysctl vm.mmap_min_addr >>>> vm.mmap_min_addr = 65536 >>>> >>>> usually prohibits it for good reason. >>>> >>>>> This has to do more with the ABI I had for pkvm and shared memory >>>>> implementations, in which you don't need to specify the userspace >>>>> address for memory in a guestmem memslot. The issue is there is no >>>>> obvious address to map it to. This would be the case in kvm:arm64 for >>>>> tracking paravirtualized time, which the userspace doesn't necessarily >>>>> need to interact with, but kvm does. >>>> >>>> So I understand correctly: userspace wouldn't have to mmap it because it >>>> is not interested in accessing it, but there is nothing speaking against >>>> mmaping it, at least in the first shot. >>>> >>>> I assume it would not be a private memslot (so far, my understanding is >>>> that internal memslots never have a guest_memfd attached). >>>> kvm_gmem_create() is only called via KVM_CREATE_GUEST_MEMFD, to be set >>>> on user-created memslots. >>>> >>>>> >>>>> That said, we could always have a userspace address dedicated to >>>>> mapping shared locations, and use that address when the necessity >>>>> arises. Or we could always require that memslots have a userspace >>>>> address, even if not used. I don't really have a strong preference. >>>> >>>> So, the simpler version where user space would simply mmap guest_memfd >>>> to provide the address via userspace_addr would at least work for the >>>> use case of paravirtualized time? >>> >>> fwiw, I'm currently prototyping something like this for x86 (although >>> not by putting the gmem address into userspace_addr, but by adding a new >>> field to memslots, so that memory attributes continue working), based on >>> what we talked about at the last guest_memfd sync meeting (the whole >>> "how to get MMIO emulation working for non-CoCo VMs in guest_memfd" >>> story). So I guess if we're going down this route for x86, maybe it >>> makes sense to do the same on ARM, for consistency? >>> >>>> It would get rid of the immediate need for this patch and patch #4 to >>>> get it flying. >>>> >>>> >>>> One interesting question is: when would you want shared memory in >>>> guest_memfd and *not* provide it as part of the same memslot. >>> >>> In my testing of non-CoCo gmem VMs on ARM, I've been able to get quite >>> far without giving KVM a way to internally access shared parts of gmem - >>> it's why I was probing Fuad for this simplified series, because >>> KVM_SW_PROTECTED_VM + mmap (for loading guest kernel) is enough to get a >>> working non-CoCo VM on ARM (although I admittedly never looked at clocks >>> inside the guest - maybe that's one thing that breaks if KVM can't >>> access gmem. How to guest and host agree on the guest memory range >>> used to exchange paravirtual timekeeping information? Could that exchange >>> be intercepted in userspace, and set to shared via memory attributes (e.g. >>> placed outside gmem)? That's the route I'm going down the paravirtual >>> time on x86). >> >> For an idea of what it looks like on arm64, here's how kvmtool handles it: >> https://github.com/kvmtool/kvmtool/blob/master/arm/aarch64/pvtime.c >> >> Cheers, >> /fuad > > Thanks! In that example, kvmtool actually allocates a separate memslot for > the pvclock stuff, so I guess it's always possible to simply put it into > a non-gmem memslot, which indeed sidesteps this issue as you mention in > your reply to David :D Does that work on CC where all memory defaults to private first, and the VM explicitly has to opt into marking it shared first, or how exactly would the flow of operations be in the cases of the non-gmem ("good old") memslot? -- Cheers, David / dhildenb