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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18310C433FE for ; Wed, 16 Nov 2022 19:07:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232506AbiKPTHH (ORCPT ); Wed, 16 Nov 2022 14:07:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229724AbiKPTHG (ORCPT ); Wed, 16 Nov 2022 14:07:06 -0500 Received: from mail-wm1-x32e.google.com (mail-wm1-x32e.google.com [IPv6:2a00:1450:4864:20::32e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 656F36035C for ; Wed, 16 Nov 2022 11:07:02 -0800 (PST) Received: by mail-wm1-x32e.google.com with SMTP id v7so12602156wmn.0 for ; Wed, 16 Nov 2022 11:07:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:from:to:cc:subject:date :message-id:reply-to; bh=RrIEWhRQRlR3NVC7xZs7jfrYAvxywp8v6T2LfNTij+Q=; b=Jx3yqn06j6rS5Fs5NvtNZW3afRbtKDAjyYZ/cbyT5J0fw+x5DSiBa34zecJ2zXBEP6 dXVq49aZkpeYNlw8FZCjejz+X8sYE98oXGoc760qT01ItS+LpGXs0KR6luYi6XidGGnJ izQy2tFtJsUmRdujni2tPVUtXn9CPZshGLwHnmOZlDGECGPB/n+QnPoJLt8dAH9evwNe fhOCmkSkLWIbZ04JJ1cM5aaZNcxxY3L6QunV484wNTFteoVmyskDXedR8UqBBpqCdgYP ARhbe6kOrZMHvVRuGOwhLHdlqHzOAwDs9awbU2PksEIQB6p43e6EtlScRKP2mnLQYKXa PFRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=RrIEWhRQRlR3NVC7xZs7jfrYAvxywp8v6T2LfNTij+Q=; b=1Sv68sI6CRXEX2JXpr41NuiQFtbh0G+Me0WKeZ7/HL18vRM1xKTdi2dq0SaEfB7Rhq VtrBH3TWvPvbpPPMXnQq6zGJGaeq+TXpcZfbnBpD279qMEXedYCuqw6m6we2ld0ba42V 8PSUKFI+ZXqNk+7ovpVDqhBi4fDLNV9UOsZV2AQkBl3QM5Vn9Q71DLu4YfrRdhUvIN+7 eR9VLsjnpVz3FKYIR9fouMzN5NTtwr30H4623a0RaLETerbnPtqlVL7ZTdM4Hp0NIGKS nC0mucL9P28Agh8j0IvRfm9UJQDxJf2Yc5jBhBZdHaMSJ5syn7H3W/ljGo3wFNS42ivG awEg== X-Gm-Message-State: ANoB5pmUIc9+yr+nIHhkW2Iug7MHBzpMm6dUPYOhKFd/DHPqbIaGWMdY ct8QNvneuN6Km7jXoLC5jDTXrA== X-Google-Smtp-Source: AA0mqf5UxIGeoP/5D5Yx/z21S7fh+uGiPqn06sMVoycK8I50cpSvwpmmKvt4/Ece9ChnPUGalp4tAQ== X-Received: by 2002:a05:600c:3d0c:b0:3cf:f66c:9246 with SMTP id bh12-20020a05600c3d0c00b003cff66c9246mr2115368wmb.27.1668625620910; Wed, 16 Nov 2022 11:07:00 -0800 (PST) Received: from zen.linaroharston ([185.81.254.11]) by smtp.gmail.com with ESMTPSA id p13-20020adfe60d000000b00236e9755c02sm15976702wrm.111.2022.11.16.11.07.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Nov 2022 11:07:00 -0800 (PST) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id BDA921FFB7; Wed, 16 Nov 2022 19:06:59 +0000 (GMT) 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> User-agent: mu4e 1.9.2; emacs 28.2.50 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Chao Peng 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 Date: Wed, 16 Nov 2022 19:03:49 +0000 In-reply-to: <20221116031441.GA364614@chaop.bj.intel.com> Message-ID: <87mt8q90rw.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Chao Peng writes: > On Tue, Nov 15, 2022 at 04:56:12PM +0000, Alex Benn=C3=A9e wrote: >>=20 >> Chao Peng writes: >>=20 >> > 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/a= pi.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 users= pace 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. >> >=20=20 >> > +:: >> > + >> > + /* 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 VC= PU 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 me= mory >> > +properties of the exit. >> > + >> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is cause= d by >> > + private memory access when the bit is set. Otherwise the memory er= ror is >> > + caused by shared memory access when the bit is clear. >>=20 >> 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) which would allow you to signal the various failure modes of the shared region, or that you had accessed private memory. > >>=20 >> 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 >>=20 >> > + >> > +'gpa' and 'size' indicate the memory range the error occurs at. The u= serspace >> > +may handle the error and return to KVM to retry the previous memory a= ccess. >> > + >> > :: >> >=20=20 >> > /* 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 >> >=20=20 >> > /* 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]; >> > }; >>=20 >>=20 >> --=20 >> Alex Benn=C3=A9e --=20 Alex Benn=C3=A9e