Commit ec5be88a authored by Jing Liu's avatar Jing Liu Committed by Paolo Bonzini
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJing Liu <jing2.liu@intel.com>
Signed-off-by: default avatarKevin Tian <kevin.tian@intel.com>
Signed-off-by: default avatarYang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-13-yang.zhong@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 1df4fd83

arch/x86/kvm/vmx/vmcs.h

+5 −0
Original line number Diff line number Diff line
@@ -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)

{

arch/x86/kvm/vmx/vmx.c

+48 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ 
#include <asm/debugreg.h>

#include <asm/desc.h>

#include <asm/fpu/api.h>

#include <asm/fpu/xstate.h>

#include <asm/idtentry.h>

#include <asm/io.h>

#include <asm/irq_remapping.h>
@@ -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();

arch/x86/kvm/x86.c

+6 −0
Original line number Diff line number Diff line
@@ -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.