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 2A140C4332F for ; Thu, 17 Nov 2022 13:49:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9ABAE6B0071; Thu, 17 Nov 2022 08:49:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 95B6B6B0072; Thu, 17 Nov 2022 08:49:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 823278E0001; Thu, 17 Nov 2022 08:49:57 -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 715116B0071 for ; Thu, 17 Nov 2022 08:49:57 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 20EBA80D00 for ; Thu, 17 Nov 2022 13:49:57 +0000 (UTC) X-FDA: 80143067634.19.9ACB5ED Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by imf24.hostedemail.com (Postfix) with ESMTP id 70BF0180012 for ; Thu, 17 Nov 2022 13:49:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1668692996; x=1700228996; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:content-transfer-encoding:in-reply-to; bh=ATWbZUoO3rElYdzopyRvM0E2TkDOWFkdmG1eTQn7t9g=; b=VIWMqYu6Vk2yCnSMAmjwNmGfiU6viRbN5D7DtoHVb+VaIU0py1Tg7YzP WcQ+PkbrEzs51Ie0pBhaWlEvw9dVxacgDRBAG+O3EMuW3DDGFCVrc55ea F3LGDADWvx+oPza8I/oYPpnktRQKs+kHqvu7rUkx4f3RutupkJuIiEcto QfSX+RcGAfU4j+cLpqN6KwOpz9SzSbvc6H+4xPkFAmu57vzdGP00TDd6K C2p8DF4wAwRu51UkMaSed938A/GsYxx8mdnCFYQ7HxBr4o+VZYg46PLfA 8go+wOVxe3i3QpFFEJLOAKLAPj4Vv9XNVonpTzuXBksR3d651293GxPuM g==; X-IronPort-AV: E=McAfee;i="6500,9779,10534"; a="312865737" X-IronPort-AV: E=Sophos;i="5.96,171,1665471600"; d="scan'208";a="312865737" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Nov 2022 05:49:55 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10534"; a="670927648" X-IronPort-AV: E=Sophos;i="5.96,171,1665471600"; d="scan'208";a="670927648" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga008.jf.intel.com with ESMTP; 17 Nov 2022 05:49:44 -0800 Date: Thu, 17 Nov 2022 21:45:20 +0800 From: Chao Peng To: Alex =?iso-8859-1?Q?Benn=E9e?= Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , tabba@google.com, Michael Roth , mhocko@suse.com, Muchun Song , wei.w.wang@intel.com Subject: Re: [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Message-ID: <20221117134520.GD422408@chaop.bj.intel.com> Reply-To: Chao Peng References: <20221025151344.3784230-1-chao.p.peng@linux.intel.com> <20221025151344.3784230-4-chao.p.peng@linux.intel.com> <87cz9o9mr8.fsf@linaro.org> <20221116031441.GA364614@chaop.bj.intel.com> <87mt8q90rw.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87mt8q90rw.fsf@linaro.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668692996; a=rsa-sha256; cv=none; b=ehMxXaYTZ2KdwzKdMPIpotpDhGHi6xc8S/wI3BX/uYuYr1kcMc/6Q+nRsCUlsvMTIQ3ZTE QJWRfYk36TrQYcwQ3FmGDcNgUBtzkiZNRs8gCXnFf3n/VpK61/AuKH1FBsUMZUDRJs4IyO /cfmfbsk8kNCKSQacFfL6qGhmmUZpno= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=VIWMqYu6; spf=none (imf24.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 192.55.52.115) smtp.mailfrom=chao.p.peng@linux.intel.com; dmarc=fail reason="No valid SPF" header.from=intel.com (policy=none) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668692996; h=from:from:sender:reply-to: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=cuzsYaYjTNgYQ5FBX1gN8VtXZ8dDWEw/ACpcfAE3cm0=; b=px7d3GARcjc70yGF6Dv9reHQPT186Jm8zcinR7ibxGEkdsXJGMr4WKbH6NmsPhwQskcEoa W67a0vBzX9Hf92siYeHDyzzHuBkj/+O0QyVpDnNd4bkZoTsSzUuMDSlayoKvCWXSm2P0Yq S2YK1G1Hd2/gQVKesHGntVjNfdOYDoc= X-Stat-Signature: 8g18zwzb5s4rr5717zyq6wj1hyb1aqf7 X-Rspamd-Queue-Id: 70BF0180012 Authentication-Results: imf24.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=VIWMqYu6; spf=none (imf24.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 192.55.52.115) smtp.mailfrom=chao.p.peng@linux.intel.com; dmarc=fail reason="No valid SPF" header.from=intel.com (policy=none) X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1668692996-602258 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: On Wed, Nov 16, 2022 at 07:03:49PM +0000, Alex Bennée wrote: > > Chao Peng writes: > > > On Tue, Nov 15, 2022 at 04:56:12PM +0000, Alex Bennée wrote: > >> > >> Chao Peng writes: > >> > >> > This new KVM exit allows userspace to handle memory-related errors. It > >> > indicates an error happens in KVM at guest memory range [gpa, gpa+size). > >> > The flags includes additional information for userspace to handle the > >> > error. Currently bit 0 is defined as 'private memory' where '1' > >> > indicates error happens due to private memory access and '0' indicates > >> > error happens due to shared memory access. > >> > > >> > When private memory is enabled, this new exit will be used for KVM to > >> > exit to userspace for shared <-> private memory conversion in memory > >> > encryption usage. In such usage, typically there are two kind of memory > >> > conversions: > >> > - explicit conversion: happens when guest explicitly calls into KVM > >> > to map a range (as private or shared), KVM then exits to userspace > >> > to perform the map/unmap operations. > >> > - implicit conversion: happens in KVM page fault handler where KVM > >> > exits to userspace for an implicit conversion when the page is in a > >> > different state than requested (private or shared). > >> > > >> > Suggested-by: Sean Christopherson > >> > Co-developed-by: Yu Zhang > >> > Signed-off-by: Yu Zhang > >> > Signed-off-by: Chao Peng > >> > --- > >> > Documentation/virt/kvm/api.rst | 23 +++++++++++++++++++++++ > >> > include/uapi/linux/kvm.h | 9 +++++++++ > >> > 2 files changed, 32 insertions(+) > >> > > >> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > >> > index f3fa75649a78..975688912b8c 100644 > >> > --- a/Documentation/virt/kvm/api.rst > >> > +++ b/Documentation/virt/kvm/api.rst > >> > @@ -6537,6 +6537,29 @@ array field represents return values. The userspace should update the return > >> > values of SBI call before resuming the VCPU. For more details on RISC-V SBI > >> > spec refer, https://github.com/riscv/riscv-sbi-doc. > >> > > >> > +:: > >> > + > >> > + /* KVM_EXIT_MEMORY_FAULT */ > >> > + struct { > >> > + #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0) > >> > + __u32 flags; > >> > + __u32 padding; > >> > + __u64 gpa; > >> > + __u64 size; > >> > + } memory; > >> > + > >> > +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has > >> > +encountered a memory error which is not handled by KVM kernel module and > >> > +userspace may choose to handle it. The 'flags' field indicates the memory > >> > +properties of the exit. > >> > + > >> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by > >> > + private memory access when the bit is set. Otherwise the memory error is > >> > + caused by shared memory access when the bit is clear. > >> > >> What does a shared memory access failure entail? > > > > In the context of confidential computing usages, guest can issue a > > shared memory access while the memory is actually private from the host > > point of view. This exit with bit 0 cleared gives userspace a chance to > > convert the private memory to shared memory on host. > > I think this should be explicit rather than implied by the absence of > another flag. Sean suggested you might want flags for RWX failures so > maybe something like: > > KVM_MEMORY_EXIT_SHARED_FLAG_READ (1 << 0) > KVM_MEMORY_EXIT_SHARED_FLAG_WRITE (1 << 1) > KVM_MEMORY_EXIT_SHARED_FLAG_EXECUTE (1 << 2) > KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 3) Yes, but I would not add 'SHARED' to RWX, they are not share memory specific, private memory can also set them once introduced. Thanks, Chao > > which would allow you to signal the various failure modes of the shared > region, or that you had accessed private memory. > > > > >> > >> If you envision any other failure modes it might be worth making it > >> explicit with additional flags. > > > > Sean mentioned some more usages[1][]2] other than the memory conversion > > for confidential usage. But I would leave those flags being added in the > > future after those usages being well discussed. > > > > [1] https://lkml.kernel.org/r/20200617230052.GB27751@linux.intel.com > > [2] https://lore.kernel.org/all/YKxJLcg%2FWomPE422@google.com > > > >> I also wonder if a bitmask makes sense if > >> there can only be one reason for a failure? Maybe all that is needed is > >> a reason enum? > > > > Tough we only have one reason right now but we still want to leave room > > for future extension. Enum can express a single value at once well but > > bitmask makes it possible to express multiple orthogonal flags. > > I agree if multiple orthogonal failures can occur at once a bitmask is > the right choice. > > > > > Chao > >> > >> > + > >> > +'gpa' and 'size' indicate the memory range the error occurs at. The userspace > >> > +may handle the error and return to KVM to retry the previous memory access. > >> > + > >> > :: > >> > > >> > /* KVM_EXIT_NOTIFY */ > >> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > >> > index f1ae45c10c94..fa60b032a405 100644 > >> > --- a/include/uapi/linux/kvm.h > >> > +++ b/include/uapi/linux/kvm.h > >> > @@ -300,6 +300,7 @@ struct kvm_xen_exit { > >> > #define KVM_EXIT_RISCV_SBI 35 > >> > #define KVM_EXIT_RISCV_CSR 36 > >> > #define KVM_EXIT_NOTIFY 37 > >> > +#define KVM_EXIT_MEMORY_FAULT 38 > >> > > >> > /* For KVM_EXIT_INTERNAL_ERROR */ > >> > /* Emulate instruction failed. */ > >> > @@ -538,6 +539,14 @@ struct kvm_run { > >> > #define KVM_NOTIFY_CONTEXT_INVALID (1 << 0) > >> > __u32 flags; > >> > } notify; > >> > + /* KVM_EXIT_MEMORY_FAULT */ > >> > + struct { > >> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0) > >> > + __u32 flags; > >> > + __u32 padding; > >> > + __u64 gpa; > >> > + __u64 size; > >> > + } memory; > >> > /* Fix the size of the union. */ > >> > char padding[256]; > >> > }; > >> > >> > >> -- > >> Alex Bennée > > > -- > Alex Bennée