From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 2B1611DFE11 for ; Thu, 17 Oct 2024 17:55:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729187715; cv=none; b=gdBgEAOxUGenL50sweufzfhT359yZgrmP0tLX6UKKSV8aCB7oUhJWQGET9wXOtMuKpPDSbt5iOwoZ7uVEYyGRoifwIHLieN4YVW9u3o5qusyjiBizV9z4Mb45smLp/b7RMP7eKKW6ZNIrzRXNfO14je/Mh7xXvNIv84yYVYNPW4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729187715; c=relaxed/simple; bh=mMcsp/iMlAmoBKZKBMJoWh4WxLSeWmI4w7731hcUnKI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BRoOHkYUmJEShWtSf0+kNM2U38qybNIEh+mGMA8ByZvymiOlVGMoKEcyHy+iR241tOSDp2E8E5trH91psRGB7c3cXEUEbzaom2Edgy6oPa4IGRtgo74JmZ53xo8ugwjsNKdYINHO1P03YCtgotWKUy8f9fGuRJjWVNJXirDdRzA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=WlK0B10J; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WlK0B10J" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729187713; 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=DTYljF8POalugMXuFvWjkYZLAf4we1kA3NrQt2GmKV4=; b=WlK0B10JbbQ578yMMIQmLnKiF4bBTm6pnIbJxTiEhPlWVivkSoblPDnydnQjF2o4Jbl/dN bH4MsRHVNj/HQrn4+DNjH/6fMCURiiqFmfgk6mZyxlzj4XduwqPUZzAFt9QuEtCWYC1X01 QMnn/dYCigtM6ZjEtAC3q7KnA8WsVY4= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-530-3wVuuKUsPPqCISZtE8pA5A-1; Thu, 17 Oct 2024 13:55:12 -0400 X-MC-Unique: 3wVuuKUsPPqCISZtE8pA5A-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-43159c07193so10045425e9.0 for ; Thu, 17 Oct 2024 10:55:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1729187711; x=1729792511; 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=DTYljF8POalugMXuFvWjkYZLAf4we1kA3NrQt2GmKV4=; b=oHHFchL50X861Wo1b1ZkM6jdDSZQmZ1lDEJW5ChKFHf5aPPiiuan7rKpaNq8KBgf7X /eiIdzavJpyQw9NnH/VPBYVF2BW5BbTEJc8vEpbVfTtW7GVnPNAllx2DsrIGUtKHtKsf qTfxxfkS7ttiEZLwzfveqD0divoY3wmZCt2AJ9SiG7+1KRn94v3bGoI6REufmlLy8LUI lmWSaSJfPDVd/B3WI2MNrTNIr+PAsLQcwPotCBU5qU7XI18ddbDfv3zriOOA/N3KbHQD 2orTvTm5H+gUzFBp04XpS+ADMwlH/V55ltKIJxQ6YI4iBpFTrpG2NIE1Ky4DEjMoECM3 lTvw== X-Forwarded-Encrypted: i=1; AJvYcCXUMS07+tZS/l+bLdSSsIt02j35scgtSldFBKCgNZuhm8dr8fxixHXR75FWAdOC9yonshSarecpip3UaJU+D6w=@vger.kernel.org X-Gm-Message-State: AOJu0YyODOMbnIWQ5A7oAq4aXHYRSDOKqS94LzvUPacoz/ZiFOGKANNz ZLyCrsyb0x0hgn0oPOE92xucb8xhadBFzpriBzfr6A5hYqZVNyge6Yw1FiMIR65TezDFXjD/sQK PTq5bdQxqnDmZlg+QsJw/xaGymm9re2RzXME250Z/gG6HGEGqkXvj8d10RfneIlE2rQ== X-Received: by 2002:a05:600c:3b8e:b0:431:24c3:dbaa with SMTP id 5b1f17b1804b1-431255cea47mr208054045e9.2.1729187710693; Thu, 17 Oct 2024 10:55:10 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEHnxbUQfWueTkDkaivXXE1yKf5gKXrsNzTMq1SSj058gURZUSa2g/DuU7vFomh7hQIpIbadg== X-Received: by 2002:a05:600c:3b8e:b0:431:24c3:dbaa with SMTP id 5b1f17b1804b1-431255cea47mr208053525e9.2.1729187710262; Thu, 17 Oct 2024 10:55:10 -0700 (PDT) Received: from ?IPV6:2003:cb:c705:7600:62cc:24c1:9dbe:a2f5? (p200300cbc705760062cc24c19dbea2f5.dip0.t-ipconnect.de. [2003:cb:c705:7600:62cc:24c1:9dbe:a2f5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431606940e9sm2562995e9.19.2024.10.17.10.55.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Oct 2024 10:55:09 -0700 (PDT) Message-ID: <9cee402b-eea0-4a66-870b-d2bc7a137c9f@redhat.com> Date: Thu, 17 Oct 2024 19:55:06 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 26/39] KVM: guest_memfd: Track faultability within a struct kvm_gmem_private To: Jason Gunthorpe Cc: Peter Xu , Ackerley Tng , tabba@google.com, quic_eberman@quicinc.com, roypat@amazon.co.uk, rientjes@google.com, fvdl@google.com, jthoughton@google.com, seanjc@google.com, pbonzini@redhat.com, zhiquan1.li@intel.com, fan.du@intel.com, jun.miao@intel.com, isaku.yamahata@intel.com, muchun.song@linux.dev, erdemaktas@google.com, vannapurve@google.com, qperret@google.com, jhubbard@nvidia.com, willy@infradead.org, shuah@kernel.org, brauner@kernel.org, bfoster@redhat.com, kent.overstreet@linux.dev, pvorel@suse.cz, rppt@kernel.org, richard.weiyang@gmail.com, anup@brainfault.org, haibo1.xu@intel.com, ajones@ventanamicro.com, vkuznets@redhat.com, maciej.wieczor-retman@intel.com, pgonda@google.com, oliver.upton@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <1d243dde-2ddf-4875-890d-e6bb47931e40@redhat.com> <20241016225157.GQ3559746@nvidia.com> <20241016235424.GU3559746@nvidia.com> <20241017164713.GF3559746@nvidia.com> <20241017171639.GN3559746@nvidia.com> From: David Hildenbrand Content-Language: en-US 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: <20241017171639.GN3559746@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.10.24 19:16, Jason Gunthorpe wrote: > On Thu, Oct 17, 2024 at 07:11:46PM +0200, David Hildenbrand wrote: >> On 17.10.24 18:47, Jason Gunthorpe wrote: >>> On Thu, Oct 17, 2024 at 10:58:29AM -0400, Peter Xu wrote: >>> >>>> My question was more torwards whether gmemfd could still expose the >>>> possibility to be used in VA forms to other modules that may not support >>>> fd+offsets yet. >>> >>> I keep hearing they don't want to support page pinning on a guestmemfd >>> mapping, so VA based paths could not work. >> >> For shared pages it absolutely must work. That's what I keep hearing :) > > Oh that's confusing. I assume non longterm pins desired on shared > pages though?? For user space to driver I/O to shared pages GUP is often required (e.g., O_DIRECT), as was raised at LPC in a session IIRC (someone brought up a use case that involved vhost-user and friends). Of course, for the guest_memfd use cases where we want to remove also shared pages from the directmap, it's not possible, but let's put that aside (I recall there was a brief discussion at LPC about that: it's tricky for shared memory for exactly this reason -- I/O). longterm pins would have to be used with care, and it's under user-space control, and user-space must be aware of the implications: for example, registering shared pages as fixed buffers for liburing is possible, but when a conversion to private is requested it must unregister these buffers. (in VFIO terms, a prior unmap operation would be required) Of course, a conversion to private will not work as long as the pages are pinned, and this is under user space control. If the guest attempts to perform such a conversion while pages will be pinned, there will likely be a notification to user space (we touched on that today in the upstream call) that something is blocking the conversion of that page, and user space has to fix that up and retry. It's not expected to matter much in practice, but it can be triggered and there must be a way to handle it: if a guest triggers a shared->private conversion while there is still I/O going on the page, something is messed up, and the conversion will be delayed until the I/O is done and the page can be converted. There are still quite some things to be clarified, but this is my understanding so far. -- Cheers, David / dhildenb