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([2601:646:c200:1ef2:1d60:88a3:44d6:6b86]) by smtp.gmail.com with ESMTPSA id c5sm3109142pjo.4.2021.01.12.07.22.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Jan 2021 07:22:42 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions Date: Tue, 12 Jan 2021 07:22:41 -0800 Message-Id: References: <9f3b8e3dca453c13867c5c6b61645b9b58d68f61.camel@redhat.com> Cc: Vitaly Kuznetsov , Wei Huang , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com, joro@8bytes.org, bp@alien8.de, tglx@linutronix.de, mingo@redhat.com, x86@kernel.org, jmattson@google.com, wanpengli@tencent.com, bsd@redhat.com, dgilbert@redhat.com In-Reply-To: <9f3b8e3dca453c13867c5c6b61645b9b58d68f61.camel@redhat.com> To: Maxim Levitsky X-Mailer: iPhone Mail (18C66) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jan 12, 2021, at 7:17 AM, Maxim Levitsky wrote: >=20 > =EF=BB=BFOn Tue, 2021-01-12 at 07:11 -0800, Andy Lutomirski wrote: >>>> On Jan 12, 2021, at 4:15 AM, Vitaly Kuznetsov wro= te: >>>=20 >>> =EF=BB=BFWei Huang writes: >>>=20 >>>> From: Bandan Das >>>>=20 >>>> While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD >>>> CPUs check EAX against reserved memory regions (e.g. SMM memory on host= ) >>>> before checking VMCB's instruction intercept. If EAX falls into such >>>> memory areas, #GP is triggered before VMEXIT. This causes problem under= >>>> nested virtualization. To solve this problem, KVM needs to trap #GP and= >>>> check the instructions triggering #GP. For VM execution instructions, >>>> KVM emulates these instructions; otherwise it re-injects #GP back to >>>> guest VMs. >>>>=20 >>>> Signed-off-by: Bandan Das >>>> Co-developed-by: Wei Huang >>>> Signed-off-by: Wei Huang >>>> --- >>>> arch/x86/include/asm/kvm_host.h | 8 +- >>>> arch/x86/kvm/mmu.h | 1 + >>>> arch/x86/kvm/mmu/mmu.c | 7 ++ >>>> arch/x86/kvm/svm/svm.c | 157 +++++++++++++++++++------------- >>>> arch/x86/kvm/svm/svm.h | 8 ++ >>>> arch/x86/kvm/vmx/vmx.c | 2 +- >>>> arch/x86/kvm/x86.c | 37 +++++++- >>>> 7 files changed, 146 insertions(+), 74 deletions(-) >>>>=20 >>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm= _host.h >>>> index 3d6616f6f6ef..0ddc309f5a14 100644 >>>> --- a/arch/x86/include/asm/kvm_host.h >>>> +++ b/arch/x86/include/asm/kvm_host.h >>>> @@ -1450,10 +1450,12 @@ extern u64 kvm_mce_cap_supported; >>>> * due to an intercepted #UD (see EMULTYPE_TRAP_UD). >>>> * Used to test the full emulator from userspace. >>>> * >>>> - * EMULTYPE_VMWARE_GP - Set when emulating an intercepted #GP for VMwa= re >>>> + * EMULTYPE_PARAVIRT_GP - Set when emulating an intercepted #GP for VM= ware >>>> * backdoor emulation, which is opt in via module param. >>>> * VMware backoor emulation handles select instructions >>>> - * and reinjects the #GP for all other cases. >>>> + * and reinjects #GP for all other cases. This also >>>> + * handles other cases where #GP condition needs to be >>>> + * handled and emulated appropriately >>>> * >>>> * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, i= n which >>>> * case the CR2/GPA value pass on the stack is valid. >>>> @@ -1463,7 +1465,7 @@ extern u64 kvm_mce_cap_supported; >>>> #define EMULTYPE_SKIP (1 << 2) >>>> #define EMULTYPE_ALLOW_RETRY_PF (1 << 3) >>>> #define EMULTYPE_TRAP_UD_FORCED (1 << 4) >>>> -#define EMULTYPE_VMWARE_GP (1 << 5) >>>> +#define EMULTYPE_PARAVIRT_GP (1 << 5) >>>> #define EMULTYPE_PF (1 << 6) >>>>=20 >>>> int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);= >>>> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h >>>> index 581925e476d6..1a2fff4e7140 100644 >>>> --- a/arch/x86/kvm/mmu.h >>>> +++ b/arch/x86/kvm/mmu.h >>>> @@ -219,5 +219,6 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu)= ; >>>>=20 >>>> int kvm_mmu_post_init_vm(struct kvm *kvm); >>>> void kvm_mmu_pre_destroy_vm(struct kvm *kvm); >>>> +bool kvm_is_host_reserved_region(u64 gpa); >>>=20 >>> Just a suggestion: "kvm_gpa_in_host_reserved()" maybe?=20 >>>=20 >>>> #endif >>>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c >>>> index 6d16481aa29d..c5c4aaf01a1a 100644 >>>> --- a/arch/x86/kvm/mmu/mmu.c >>>> +++ b/arch/x86/kvm/mmu/mmu.c >>>> @@ -50,6 +50,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include "trace.h" >>>>=20 >>>> extern bool itlb_multihit_kvm_mitigation; >>>> @@ -5675,6 +5676,12 @@ void kvm_mmu_slot_set_dirty(struct kvm *kvm, >>>> } >>>> EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty); >>>>=20 >>>> +bool kvm_is_host_reserved_region(u64 gpa) >>>> +{ >>>> + return e820__mbapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED); >>>> +} >>>=20 >>> While _e820__mapped_any()'s doc says '.. checks if any part of the >>> range is mapped ..' it seems to me that the real check is >>> [start, end) so we should use 'gpa' instead of 'gpa-1', no? >>=20 >> Why do you need to check GPA at all? >>=20 > To reduce the scope of the workaround. >=20 > The errata only happens when you use one of SVM instructions > in the guest with EAX that happens to be inside one > of the host reserved memory regions (for example SMM). This code reduces the scope of the workaround at the cost of increasing the c= omplexity of the workaround and adding a nonsensical coupling between KVM an= d host details and adding an export that really doesn=E2=80=99t deserve to b= e exported. Is there an actual concrete benefit to this check?