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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: Tue, 15 Nov 2022 16:56:12 +0000 In-reply-to: <20221025151344.3784230-4-chao.p.peng@linux.intel.com> Message-ID: <87cz9o9mr8.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668531598; a=rsa-sha256; cv=none; b=vELglYB8XOHZAZ82i/A/uniTC8bZpvhYexcUIHXE5g4W78NiyI+RhAZcARF8ByDT/BFHaY IGgDNJJi5UDX1OltqW7djjYZDBKgJTfoXatqw/DXV7VB8LBO9B762JlpgDggskVXeo4rj/ HhTPYLLFeZMhN0T6VHBUOsH7v/1ARqM= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=linaro.org header.s=google header.b=UqienqYR; spf=pass (imf28.hostedemail.com: domain of alex.bennee@linaro.org designates 209.85.221.45 as permitted sender) smtp.mailfrom=alex.bennee@linaro.org; dmarc=pass (policy=none) header.from=linaro.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668531598; h=from:from:sender: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=mfMmr+1QjnU4sjisGoRqb8FxQFwgEIl76i25CgDhNpM=; b=YONmpDSa43ripzAUtC8r7e6lnkExrYyy1ZLUCVWpeABWI7RXZLl7dLJsAT1GsGfSepgWyW P2J/IY3ycjbsL8YHsXIntnq+axk3OKSoaCwImSWTD8HjMWyd25XbAfhmA2wShu2FkqEGrC ai+/9iPppxVmCvJQH1t2hhSISpHbvk4= X-Stat-Signature: e9fdj66fzub99auuu1ixokyryq66x6xk X-Rspamd-Queue-Id: 354B2C000E Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=linaro.org header.s=google header.b=UqienqYR; spf=pass (imf28.hostedemail.com: domain of alex.bennee@linaro.org designates 209.85.221.45 as permitted sender) smtp.mailfrom=alex.bennee@linaro.org; dmarc=pass (policy=none) header.from=linaro.org X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1668531597-379791 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: 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 userspac= e 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 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? If you envision any other failure modes it might be worth making it explicit with additional flags. 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? > + > +'gpa' and 'size' indicate the memory range the error occurs at. The user= space > +may handle the error and return to KVM to retry the previous memory acce= ss. > + > :: >=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 Alex Benn=C3=A9e