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 370E3C4332F for ; Wed, 16 Nov 2022 03:19:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 532F36B0071; Tue, 15 Nov 2022 22:19:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4E3126B0072; Tue, 15 Nov 2022 22:19:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 383626B0073; Tue, 15 Nov 2022 22:19:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 256AC6B0071 for ; Tue, 15 Nov 2022 22:19:19 -0500 (EST) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id E4F3FAB71F for ; Wed, 16 Nov 2022 03:19:18 +0000 (UTC) X-FDA: 80137849596.07.D1F7958 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf30.hostedemail.com (Postfix) with ESMTP id 0B36180004 for ; Wed, 16 Nov 2022 03:19:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1668568758; x=1700104758; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:content-transfer-encoding:in-reply-to; bh=I/nWquwbUx6Foszq8Q3bav+jUHNq3BtFcT49kSsIgfs=; b=cif72IR8r6QnKBTn+kSqW2C8SZXIpmIqD7tiXfvhBAH2bQ85I0VLSah+ /29B5DmAKmJK0McJC9ny6UJ57evmJlsy5MAXhBc56KOZ9nKbpR1pI6oih 82A4Dt+IHOTnMSRUlpiWlr7j5ZNqnsRDJgrd3BlHlOW3JhTLKLMrfo3Ds mxxSI2Vs2r/qJ3d6pnVW1U8FIxFN7pcGrb1vwkaHA/TH9Vm+9nDyLBjMK 7Nz/P9RbHlPdxMd6RV7lPOTY4EccRI+xlCCnJ/XWDA7Aagk1UiKxXqMcI AHWkYcBbVJF6j0MILzSH7g+VHknGC4XcPX41i43cvAoEp6/bBbtAJZHQb w==; X-IronPort-AV: E=McAfee;i="6500,9779,10532"; a="314248327" X-IronPort-AV: E=Sophos;i="5.96,167,1665471600"; d="scan'208";a="314248327" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Nov 2022 19:19:16 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10532"; a="633472721" X-IronPort-AV: E=Sophos;i="5.96,167,1665471600"; d="scan'208";a="633472721" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga007.jf.intel.com with ESMTP; 15 Nov 2022 19:19:05 -0800 Date: Wed, 16 Nov 2022 11:14:41 +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: <20221116031441.GA364614@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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87cz9o9mr8.fsf@linaro.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668568758; a=rsa-sha256; cv=none; b=Ni7gDBFKLsv9ENdz+Qyv8m+1peISeLcPJfhX+YUdftWZ63j1Kiq4RpCbPOLkrQR0ptXsnD mkf+/QSw5Mz87HtDejkyaK1TnQ7po5mZW12Ax/QSZFgHnTCM3tHSCgCpvnEzJwstRCfFw/ o2wm/jWkhv2A9bNOcAPokvbAriF7UfE= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=cif72IR8; spf=none (imf30.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.65) 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=1668568758; 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=C3vIizZOfJMUZjr4jL4Xo1OTNZyqgeiUV0VH/YuYCLw=; b=LcpfzUdVWiycLp+oF0GSiwUfA6qs3yVEfyu1VMoSMs2CFdTTEASPpn9EDQVHgJk53NDWpm mptvnLTjMu//X5ER4GIfzKbeqtjCmeCpt+LiIA9/+8TeyEex3bJtsujUiCU25m3x2Z+u5z JsbVSsAJLSkqHyABnQcz4xGFOfHm8EY= X-Stat-Signature: 9ia38cqd45ezpkxrtps1atdy3648nt47 X-Rspamd-Queue-Id: 0B36180004 Authentication-Results: imf30.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=cif72IR8; spf=none (imf30.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.65) 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: 1668568757-665497 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 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. > > 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. 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