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 E9B802FAF for ; Tue, 31 Aug 2021 19:12:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1630437171; 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; bh=B3R8+9xCMOWLuSi664S67yIHwiGeNUaH36y7wRqkQk8=; b=FUZ/rXlQvZM75rOFydFPmME0oFtv5gGfsohVbJt6+t0S3qkB/FgcDZwuwAXC+2h3TsIPAH z+b3KXbrK2gx4K4mxjJaTqTzavOuyFAMmFGMqBQfuVJbZNHvhGPcrMc3Ew9z+9RmOmUrbu EnXrqXD6ymZoJO2ygWNZgnbINka5P5Y= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-260-8EaKS20zP2ylq8fH3Su8KA-1; Tue, 31 Aug 2021 15:12:47 -0400 X-MC-Unique: 8EaKS20zP2ylq8fH3Su8KA-1 Received: by mail-wr1-f69.google.com with SMTP id h14-20020a056000000e00b001575b00eb08so144946wrx.13 for ; Tue, 31 Aug 2021 12:12:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:organization :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=B3R8+9xCMOWLuSi664S67yIHwiGeNUaH36y7wRqkQk8=; b=LDbZ8OnRQYvcDLjscNun8knJE+SRiS1evbinjg8uI4YOD29PNVhviIyIkBImED9mkZ d7I0k0Ub9PH2QX+bR5OF9OSjS5J+FcuveZzWNmQ8QsULo6wERf1mz8+k9JoqlV7FIHvf ip4yCj75jvBkzgPPesNu0+CIXxLo1FJN/d88tTciv5PwSfJVCVFkjMe6n6Ba4amTMS6E OyYZPPajLFNoc8XNn08mOIyv9eUEwahUwtNq/lGeYylMtS7cMpzDZ30WVuJFwQWTQB8U /P1Jqo/xoX9VhMbUtnZIkDylS4sdNBUGTe1ndYk7L3fR7A7h7e863RE54l0UmVH8wiLl xh/Q== X-Gm-Message-State: AOAM533WufK85riHDJWCasbJUTE1pHHejrgwo6NPxmjVVHxib3Pw82RD cbCaYGZY7yKULJ6LG1zPtrS0BIot9WBENV7zPuRRpk2YABrQAsRJwQ6oeFS90mIoPS+I1PbVfAa FSiHUNoHZwqjDUWnUfy70+w== X-Received: by 2002:a1c:f315:: with SMTP id q21mr5819457wmq.76.1630437166298; Tue, 31 Aug 2021 12:12:46 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxiLNTwKQMvs3colTkzHCAECIzU7cGUrdshsPwDbRyk3ubr6ahQwvcGeQbVyq70Sw5+SV5+fA== X-Received: by 2002:a1c:f315:: with SMTP id q21mr5819425wmq.76.1630437166118; Tue, 31 Aug 2021 12:12:46 -0700 (PDT) Received: from [192.168.3.132] (p4ff23bf5.dip0.t-ipconnect.de. [79.242.59.245]) by smtp.gmail.com with ESMTPSA id f5sm3231993wmb.47.2021.08.31.12.12.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Aug 2021 12:12:45 -0700 (PDT) Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory To: Sean Christopherson , Andy Lutomirski Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm list , Linux Kernel Mailing List , Borislav Petkov , Andrew Morton , Joerg Roedel , Andi Kleen , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , "Peter Zijlstra (Intel)" , Ingo Molnar , Varad Gautam , Dario Faggioli , the arch/x86 maintainers , linux-mm@kvack.org, linux-coco@lists.linux.dev, "Kirill A. Shutemov" , "Kirill A . Shutemov" , Sathyanarayanan Kuppuswamy , Dave Hansen , Yu Zhang References: <20210824005248.200037-1-seanjc@google.com> <307d385a-a263-276f-28eb-4bc8dd287e32@redhat.com> <40af9d25-c854-8846-fdab-13fe70b3b279@kernel.org> <73319f3c-6f5e-4f39-a678-7be5fddd55f2@www.fastmail.com> From: David Hildenbrand Organization: Red Hat Message-ID: <949e6d95-266d-0234-3b86-6bd3c5267333@redhat.com> Date: Tue, 31 Aug 2021 21:12:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit On 28.08.21 00:28, Sean Christopherson wrote: > On Fri, Aug 27, 2021, Andy Lutomirski wrote: >> >> On Thu, Aug 26, 2021, at 2:26 PM, David Hildenbrand wrote: >>> On 26.08.21 19:05, Andy Lutomirski wrote: >> >>>> Oof. That's quite a requirement. What's the point of the VMA once all >>>> this is done? >>> >>> You can keep using things like mbind(), madvise(), ... and the GUP code >>> with a special flag might mostly just do what you want. You won't have >>> to reinvent too many wheels on the page fault logic side at least. > > Ya, Kirill's RFC more or less proved a special GUP flag would indeed Just Work. > However, the KVM page fault side of things would require only a handful of small > changes to send private memslots down a different path. Compared to the rest of > the enabling, it's quite minor. > > The counter to that is other KVM architectures would need to learn how to use the > new APIs, though I suspect that there will be a fair bit of arch enabling regardless > of what route we take. > >> You can keep calling the functions. The implementations working is a >> different story: you can't just unmap (pte_numa-style or otherwise) a private >> guest page to quiesce it, move it with memcpy(), and then fault it back in. > > Ya, I brought this up in my earlier reply. Even the initial implementation (without > real NUMA support) would likely be painful, e.g. the KVM TDX RFC/PoC adds dedicated > logic in KVM to handle the case where NUMA balancing zaps a _pinned_ page and then > KVM fault in the same pfn. It's not thaaat ugly, but it's arguably more invasive > to KVM's page fault flows than a new fd-based private memslot scheme. I might have a different mindset, but less code churn doesn't necessarily translate to "better approach". I'm certainly not pushing for what I proposed (it's a rough, broken sketch). I'm much rather trying to come up with alternatives that try solving the same issue, handling the identified requirements. I have a gut feeling that the list of requirements might not be complete yet. For example, I wonder if we have to protect against user space replacing private pages by shared pages or punishing random holes into the encrypted memory fd. -- Thanks, David / dhildenb