From f8fabea728f0a9cea48a99eef89880ad575538f5 Mon Sep 17 00:00:00 2001 From: Jing Liu Date: Wed, 5 Jan 2022 04:35:23 -0800 Subject: [PATCH] kvm: x86: Intercept #NM for saving IA32_XFD_ERR Guest IA32_XFD_ERR is generally modified in two places: - Set by CPU when #NM is triggered; - Cleared by guest in its #NM handler; Intercept #NM for the first case when a nonzero value is written to IA32_XFD. Nonzero indicates that the guest is willing to do dynamic fpstate expansion for certain xfeatures, thus KVM needs to manage and virtualize guest XFD_ERR properly. The vcpu exception bitmap is updated in XFD write emulation according to guest_fpu::xfd. Save the current XFD_ERR value to the guest_fpu container in the #NM VM-exit handler. This must be done with interrupt disabled, otherwise the unsaved MSR value may be clobbered by host activity. The saving operation is conducted conditionally only when guest_fpu:xfd includes a non-zero value. Doing so also avoids misread on a platform which doesn't support XFD but #NM is triggered due to L1 interception. Queueing #NM to the guest is postponed to handle_exception_nmi(). This goes through the nested_vmx check so a virtual vmexit is queued instead when #NM is triggered in L2 but L1 wants to intercept it. Restore the host value (always ZERO outside of the host #NM handler) before enabling interrupt. Restore the guest value from the guest_fpu container right before entering the guest (with interrupt disabled). Suggested-by: Thomas Gleixner Signed-off-by: Jing Liu Signed-off-by: Kevin Tian Signed-off-by: Yang Zhong Message-Id: <20220105123532.12586-13-yang.zhong@intel.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/vmcs.h | 5 +++++ arch/x86/kvm/vmx/vmx.c | 48 +++++++++++++++++++++++++++++++++++++++++ arch/x86/kvm/x86.c | 6 ++++++ 3 files changed, 59 insertions(+) diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h index 6e5de2e2b0da6..e325c290a8162 100644 --- a/arch/x86/kvm/vmx/vmcs.h +++ b/arch/x86/kvm/vmx/vmcs.h @@ -129,6 +129,11 @@ static inline bool is_machine_check(u32 intr_info) return is_exception_n(intr_info, MC_VECTOR); } +static inline bool is_nm_fault(u32 intr_info) +{ + return is_exception_n(intr_info, NM_VECTOR); +} + /* Undocumented: icebp/int1 */ static inline bool is_icebp(u32 intr_info) { diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 7b5abe25e1e5d..84f6904cdb6e2 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include #include @@ -761,6 +762,13 @@ void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu) vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, match); } + /* + * Trap #NM if guest xfd contains a non-zero value so guest XFD_ERR + * can be saved timely. + */ + if (vcpu->arch.guest_fpu.fpstate->xfd) + eb |= (1u << NM_VECTOR); + vmcs_write32(EXCEPTION_BITMAP, eb); } @@ -1967,6 +1975,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) case MSR_KERNEL_GS_BASE: vmx_write_guest_kernel_gs_base(vmx, data); break; + case MSR_IA32_XFD: + ret = kvm_set_msr_common(vcpu, msr_info); + /* Update #NM interception according to guest xfd */ + if (!ret) + vmx_update_exception_bitmap(vcpu); + break; #endif case MSR_IA32_SYSENTER_CS: if (is_guest_mode(vcpu)) @@ -4798,6 +4812,17 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu) if (is_machine_check(intr_info) || is_nmi(intr_info)) return 1; /* handled by handle_exception_nmi_irqoff() */ + /* + * Queue the exception here instead of in handle_nm_fault_irqoff(). + * This ensures the nested_vmx check is not skipped so vmexit can + * be reflected to L1 (when it intercepts #NM) before reaching this + * point. + */ + if (is_nm_fault(intr_info)) { + kvm_queue_exception(vcpu, NM_VECTOR); + return 1; + } + if (is_invalid_opcode(intr_info)) return handle_ud(vcpu); @@ -6399,6 +6424,26 @@ static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu, kvm_after_interrupt(vcpu); } +static void handle_nm_fault_irqoff(struct kvm_vcpu *vcpu) +{ + /* + * Save xfd_err to guest_fpu before interrupt is enabled, so the + * MSR value is not clobbered by the host activity before the guest + * has chance to consume it. + * + * Do not blindly read xfd_err here, since this exception might + * be caused by L1 interception on a platform which doesn't + * support xfd at all. + * + * Do it conditionally upon guest_fpu::xfd. xfd_err matters + * only when xfd contains a non-zero value. + * + * Queuing exception is done in vmx_handle_exit. See comment there. + */ + if (vcpu->arch.guest_fpu.fpstate->xfd) + rdmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err); +} + static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx) { const unsigned long nmi_entry = (unsigned long)asm_exc_nmi_noist; @@ -6407,6 +6452,9 @@ static void handle_exception_nmi_irqoff(struct vcpu_vmx *vmx) /* if exit due to PF check for async PF */ if (is_page_fault(intr_info)) vmx->vcpu.arch.apf.host_apf_flags = kvm_read_and_reset_apf_flags(); + /* if exit due to NM, handle before interrupts are enabled */ + else if (is_nm_fault(intr_info)) + handle_nm_fault_irqoff(&vmx->vcpu); /* Handle machine checks before interrupts are enabled */ else if (is_machine_check(intr_info)) kvm_machine_check(); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b18d2838606f8..bb9534590a3a9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9952,6 +9952,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) if (test_thread_flag(TIF_NEED_FPU_LOAD)) switch_fpu_return(); + if (vcpu->arch.guest_fpu.xfd_err) + wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err); + if (unlikely(vcpu->arch.switch_db_regs)) { set_debugreg(0, 7); set_debugreg(vcpu->arch.eff_db[0], 0); @@ -10015,6 +10018,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) static_call(kvm_x86_handle_exit_irqoff)(vcpu); + if (vcpu->arch.guest_fpu.xfd_err) + wrmsrl(MSR_IA32_XFD_ERR, 0); + /* * Consume any pending interrupts, including the possible source of * VM-Exit on SVM and any ticks that occur between VM-Exit and now. -- 2.39.5