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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 385BBC0015E for ; Sat, 29 Jul 2023 00:04:36 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20221208 header.b=Zp0GOXqU; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4RCPrL1hpyz3d8M for ; Sat, 29 Jul 2023 10:04:34 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20221208 header.b=Zp0GOXqU; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=flex--seanjc.bounces.google.com (client-ip=2607:f8b0:4864:20::64a; helo=mail-pl1-x64a.google.com; envelope-from=3vlfezaykdemxjfsohlttlqj.htrqnsz2uuh-ij0qnxyx.t4qfgx.twl@flex--seanjc.bounces.google.com; receiver=lists.ozlabs.org) Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4RCPqJ185Pz2yDy for ; Sat, 29 Jul 2023 10:03:37 +1000 (AEST) Received: by mail-pl1-x64a.google.com with SMTP id d9443c01a7336-1bb962ada0dso17078825ad.2 for ; Fri, 28 Jul 2023 17:03:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690589015; x=1691193815; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=rJg9MbukUkeAf25VcBnSvGPEfaUIyqqF94QJU8orhSY=; b=Zp0GOXqU9vAtanM7byzLEY1ZTAuQCQrnfrak1thKcFFHMBCZO/N4KqKDBd5I3kJffW Vh8ovzLtMVpv7R9tgjnJuitRPz0iowTqbSccpqb9sCrit8s8jZkHgE3EKWmaz9/YJybN uhR+1LBQ/EGKFm12kofvmo1N8Or8Mhd5I9QIxgAZxJjUnAncn/OfNQ+xg9V9rSfFrTW5 6+gyXWvxsDfod0XUAEoSS/aCS0HqakbjGuI1/I8BU2Uy6FDW2YJ6LrCVt60GU5GehRX5 3Ug/sPFW2Iawha4cKCkpfEtG9Mwjo7aL2M8Rz65tztUDm7ObzFqkZ6ozvUAWJtziwaLO +gKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690589015; x=1691193815; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rJg9MbukUkeAf25VcBnSvGPEfaUIyqqF94QJU8orhSY=; b=Bc6tNL5hkO3nK5xTuYezBRcn+CJnvP9HN8NqfzUCZz2/GHEAMScJ7jPD2alf1mX+RM Y17zZYLu9GCBTtyfoktqD9BQuVjBPSg2m82HOiLqB8kKF6SM4l1QDpbBscxk5VrntSAI y6SI0xve/pZlIGZGpaRoPLAz4s7HSD0t6vNPDi2W1ZGrJTH/3uYNLtlY8+UevHW/E5VN d/Iz20RqqvaUPf3dW9AT8uLpR5RfkomVK4X2a/fdc2ttwr5cLobYXSukvi0JVxz52Owm KpFnBAx1AhlIG16MEHd1MOcgIQjRz9dk6LoXYyerfEbOGjnjrRfvbkjuIq45DDAMpnxt OtNQ== X-Gm-Message-State: ABy/qLacrJ0kk472TJ/vZY5KysmIWTTLCS0ljpnMKUcWLh3dLn7IXQHg c+WQxwsxY3fbeRtNr45uye4v1ez1WDw= X-Google-Smtp-Source: APBJJlGy4rMQGFiWHQC+IuRONPQH0HvvNAt7asJXiFk+bZ/uVjfNOjPYVgrOl+x+eQJGyA+j61wbqvGP0DI= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:902:c951:b0:1ae:6895:cb96 with SMTP id i17-20020a170902c95100b001ae6895cb96mr12864pla.5.1690589014804; Fri, 28 Jul 2023 17:03:34 -0700 (PDT) Date: Fri, 28 Jul 2023 17:03:33 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230718234512.1690985-1-seanjc@google.com> <20230718234512.1690985-7-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v11 06/29] KVM: Introduce KVM_SET_USER_MEMORY_REGION2 From: Sean Christopherson To: Quentin Perret Content-Type: text/plain; charset="us-ascii" X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, David Hildenbrand , Yu Zhang , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Chao Peng , linux-riscv@lists.infradead.org, Isaku Yamahata , Paul Moore , Marc Zyngier , Huacai Chen , James Morris , "Matthew Wilcox \(Oracle\)" , Wang , Fuad Tabba , Jarkko Sakkinen , "Serge E. Hallyn" , Maciej Szmigiero , Albert Ou , Vlastimil Babka , Michael Roth , Ackerley Tng , Paul Walmsley , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Liam Merwick , linux-mips@vger.kernel.org, Oliver Upton , linu x-security-module@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Anup Patel , linux-fsdevel@vger.kernel.org, Paolo Bonzini , Andrew Morton , Vishal Annapurve , linuxppc-dev@lists.ozlabs.org, "Kirill A . Shutemov" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Jul 28, 2023, Quentin Perret wrote: > On Tuesday 18 Jul 2023 at 16:44:49 (-0700), Sean Christopherson wrote: > > --- a/include/uapi/linux/kvm.h > > +++ b/include/uapi/linux/kvm.h > > @@ -95,6 +95,16 @@ struct kvm_userspace_memory_region { > > __u64 userspace_addr; /* start of the userspace allocated memory */ > > }; > > > > +/* for KVM_SET_USER_MEMORY_REGION2 */ > > +struct kvm_userspace_memory_region2 { > > + __u32 slot; > > + __u32 flags; > > + __u64 guest_phys_addr; > > + __u64 memory_size; > > + __u64 userspace_addr; > > + __u64 pad[16]; > > Should we replace that pad[16] with: > > __u64 size; > > where 'size' is the size of the structure as seen by userspace? This is > used in other UAPIs (see struct sched_attr for example) and is a bit > more robust for future extensions (e.g. an 'old' kernel can correctly > reject a newer version of the struct with additional fields it doesn't > know about if that makes sense, etc). "flags" serves that purpose, i.e. allows userspace to opt-in to having KVM actually consume what is currently just padding. The padding is there mainly to simplify kernel/KVM code, e.g. the number of bytes that KVM needs to copy in is static. But now that I think more on this, I don't know why we didn't just unconditionally bump the size of kvm_userspace_memory_region. We tried to play games with unions and overlays, but that was a mess[*]. KVM would need to do multiple uaccess reads, but that's not a big deal. Am I missing something, or did past us just get too clever and miss the obvious solution? [*] https://lkml.kernel.org/r/Y7xrtf9FCuYRYm1q%40google.com