| Message ID | 20210126081831.570253-5-wei.huang2@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Handle #GP for SVM execution instructions | expand |
On 26/01/21 09:18, Wei Huang wrote: > Under the case of nested on nested (L0->L1->L2->L3), #GP triggered by > SVM instructions can be hided from L1. Instead the hypervisor can inject > the proper #VMEXIT to inform L1 of what is happening. Thus L1 can avoid > invoking the #GP workaround. For this reason we turns on guest VM's > X86_FEATURE_SVME_ADDR_CHK bit for KVM running inside VM to receive the > notification and change behavior. Slightly reworked commit message: KVM: SVM: Fix #GP handling for doubly-nested virtualization Under the case of nested on nested (L0, L1, L2 are all hypervisors), #GP triggered by SVM instructions can be hidden from L1. Because we do not support emulation of the vVMLOAD/VMSAVE feature, the L0 hypervisor can inject the proper #VMEXIT to inform L1 of what is happening and L1 can avoid invoking the #GP workaround. Thanks, Paolo
On Tue, 2021-01-26 at 03:18 -0500, Wei Huang wrote: > Under the case of nested on nested (L0->L1->L2->L3), #GP triggered by > SVM instructions can be hided from L1. Instead the hypervisor can > inject the proper #VMEXIT to inform L1 of what is happening. Thus L1 > can avoid invoking the #GP workaround. For this reason we turns on > guest VM's X86_FEATURE_SVME_ADDR_CHK bit for KVM running inside VM to > receive the notification and change behavior. > > Similarly we check if vcpu is under guest mode before emulating the > vmware-backdoor instructions. For the case of nested on nested, we > let the guest handle it. > > Co-developed-by: Bandan Das <bsd@redhat.com> > Signed-off-by: Bandan Das <bsd@redhat.com> > Signed-off-by: Wei Huang <wei.huang2@amd.com> > Tested-by: Maxim Levitsky <mlevitsk@redhat.com> > Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> > --- > arch/x86/kvm/svm/svm.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index f9233c79265b..83c401d2709f 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -929,6 +929,9 @@ static __init void svm_set_cpu_caps(void) > > if (npt_enabled) > kvm_cpu_cap_set(X86_FEATURE_NPT); > + > + /* Nested VM can receive #VMEXIT instead of triggering #GP */ > + kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK); > } > > /* CPUID 0x80000008 */ > @@ -2198,6 +2201,11 @@ static int svm_instr_opcode(struct kvm_vcpu *vcpu) > > static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode) > { > + const int guest_mode_exit_codes[] = { > + [SVM_INSTR_VMRUN] = SVM_EXIT_VMRUN, > + [SVM_INSTR_VMLOAD] = SVM_EXIT_VMLOAD, > + [SVM_INSTR_VMSAVE] = SVM_EXIT_VMSAVE, > + }; > int (*const svm_instr_handlers[])(struct vcpu_svm *svm) = { > [SVM_INSTR_VMRUN] = vmrun_interception, > [SVM_INSTR_VMLOAD] = vmload_interception, > @@ -2205,7 +2213,14 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode) > }; > struct vcpu_svm *svm = to_svm(vcpu); > > - return svm_instr_handlers[opcode](svm); > + if (is_guest_mode(vcpu)) { > + svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode]; > + svm->vmcb->control.exit_info_1 = 0; > + svm->vmcb->control.exit_info_2 = 0; > + > + return nested_svm_vmexit(svm); > + } else > + return svm_instr_handlers[opcode](svm); > } > > /* > @@ -2239,7 +2254,8 @@ static int gp_interception(struct vcpu_svm *svm) > * VMware backdoor emulation on #GP interception only handles > * IN{S}, OUT{S}, and RDPMC. > */ > - return kvm_emulate_instruction(vcpu, > + if (!is_guest_mode(vcpu)) > + return kvm_emulate_instruction(vcpu, > EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE); > } else > return emulate_svm_instr(vcpu, opcode); To be honest I expected the vmware backdoor fix to be in a separate patch, but I see that Paulo already took these patches so I guess it is too late. Anyway I am very happy to see this workaround merged, and see that bug disappear forever. Best regards, Maxim Levitsky
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index f9233c79265b..83c401d2709f 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -929,6 +929,9 @@ static __init void svm_set_cpu_caps(void) if (npt_enabled) kvm_cpu_cap_set(X86_FEATURE_NPT); + + /* Nested VM can receive #VMEXIT instead of triggering #GP */ + kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK); } /* CPUID 0x80000008 */ @@ -2198,6 +2201,11 @@ static int svm_instr_opcode(struct kvm_vcpu *vcpu) static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode) { + const int guest_mode_exit_codes[] = { + [SVM_INSTR_VMRUN] = SVM_EXIT_VMRUN, + [SVM_INSTR_VMLOAD] = SVM_EXIT_VMLOAD, + [SVM_INSTR_VMSAVE] = SVM_EXIT_VMSAVE, + }; int (*const svm_instr_handlers[])(struct vcpu_svm *svm) = { [SVM_INSTR_VMRUN] = vmrun_interception, [SVM_INSTR_VMLOAD] = vmload_interception, @@ -2205,7 +2213,14 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode) }; struct vcpu_svm *svm = to_svm(vcpu); - return svm_instr_handlers[opcode](svm); + if (is_guest_mode(vcpu)) { + svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode]; + svm->vmcb->control.exit_info_1 = 0; + svm->vmcb->control.exit_info_2 = 0; + + return nested_svm_vmexit(svm); + } else + return svm_instr_handlers[opcode](svm); } /* @@ -2239,7 +2254,8 @@ static int gp_interception(struct vcpu_svm *svm) * VMware backdoor emulation on #GP interception only handles * IN{S}, OUT{S}, and RDPMC. */ - return kvm_emulate_instruction(vcpu, + if (!is_guest_mode(vcpu)) + return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE); } else return emulate_svm_instr(vcpu, opcode);