path: root/arch/arm64/kvm/debug.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Debug and Guest Debug support
 *
 * Copyright (C) 2015 - Linaro Ltd
 * Author: Alex Bennée <alex.bennee@linaro.org>
 */

#include <linux/kvm_host.h>
#include <linux/hw_breakpoint.h>

#include <asm/debug-monitors.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_emulate.h>


/*
 * save/restore_guest_debug_regs
 *
 * For some debug operations we need to tweak some guest registers. As
 * a result we need to save the state of those registers before we
 * make those modifications.
 *
 * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
 * after we have restored the preserved value to the main context.
 *
 * When single-step is enabled by userspace, we tweak PSTATE.SS on every
 * guest entry. Preserve PSTATE.SS so we can restore the original value
 * for the vcpu after the single-step is disabled.
 */
static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
{
	u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

	vcpu->arch.guest_debug_preserved.mdscr_el1 = val;
	vcpu->arch.guest_debug_preserved.pstate_ss =
					(*vcpu_cpsr(vcpu) & DBG_SPSR_SS);
}

static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
{
	u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;

	vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);

	if (vcpu->arch.guest_debug_preserved.pstate_ss)
		*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
	else
		*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
}

/**
 * kvm_arm_setup_mdcr_el2 - configure vcpu mdcr_el2 value
 *
 * @vcpu:	the vcpu pointer
 *
 * This ensures we will trap access to:
 *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
 *  - Debug ROM Address (MDCR_EL2_TDRA)
 *  - OS related registers (MDCR_EL2_TDOSA)
 *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
 *  - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
 *  - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
 */
static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
{
	preempt_disable();

	/*
	 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
	 * to disable guest access to the profiling and trace buffers
	 */
	vcpu->arch.mdcr_el2 = FIELD_PREP(MDCR_EL2_HPMN,
					 *host_data_ptr(nr_event_counters));
	vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
				MDCR_EL2_TPMS |
				MDCR_EL2_TTRF |
				MDCR_EL2_TPMCR |
				MDCR_EL2_TDRA |
				MDCR_EL2_TDOSA);

	/* Is the VM being debugged by userspace? */
	if (vcpu->guest_debug)
		/* Route all software debug exceptions to EL2 */
		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;

	/*
	 * Trap debug registers if the guest doesn't have ownership of them.
	 */
	if (!kvm_guest_owns_debug_regs(vcpu))
		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;

	/* Write MDCR_EL2 directly if we're already at EL2 */
	if (has_vhe())
		write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);

	preempt_enable();
}

/**
 * kvm_arm_setup_debug - set up debug related stuff
 *
 * @vcpu:	the vcpu pointer
 *
 * This is called before each entry into the hypervisor to setup any
 * debug related registers.
 *
 * Additionally, KVM only traps guest accesses to the debug registers if
 * the guest is not actively using them. Since the guest must not interfere
 * with the hardware state when debugging the guest, we must ensure that
 * trapping is enabled whenever we are debugging the guest using the
 * debug registers.
 */

void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
{
	unsigned long mdscr;

	/* Check if we need to use the debug registers. */
	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
		/* Save guest debug state */
		save_guest_debug_regs(vcpu);

		/*
		 * Single Step (ARM ARM D2.12.3 The software step state
		 * machine)
		 *
		 * If we are doing Single Step we need to manipulate
		 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
		 * step has occurred the hypervisor will trap the
		 * debug exception and we return to userspace.
		 *
		 * If the guest attempts to single step its userspace
		 * we would have to deal with a trapped exception
		 * while in the guest kernel. Because this would be
		 * hard to unwind we suppress the guest's ability to
		 * do so by masking MDSCR_EL.SS.
		 *
		 * This confuses guest debuggers which use
		 * single-step behind the scenes but everything
		 * returns to normal once the host is no longer
		 * debugging the system.
		 */
		if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
			/*
			 * If the software step state at the last guest exit
			 * was Active-pending, we don't set DBG_SPSR_SS so
			 * that the state is maintained (to not run another
			 * single-step until the pending Software Step
			 * exception is taken).
			 */
			if (!vcpu_get_flag(vcpu, DBG_SS_ACTIVE_PENDING))
				*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
			else
				*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;

			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
			mdscr |= DBG_MDSCR_SS;
			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
		} else {
			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
			mdscr &= ~DBG_MDSCR_SS;
			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
		}

		/*
		 * Enable breakpoints and watchpoints if userspace wants them.
		 */
		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
			mdscr |= DBG_MDSCR_MDE;
			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);

		/*
		 * The OS Lock blocks debug exceptions in all ELs when it is
		 * enabled. If the guest has enabled the OS Lock, constrain its
		 * effects to the guest. Emulate the behavior by clearing
		 * MDSCR_EL1.MDE. In so doing, we ensure that host debug
		 * exceptions are unaffected by guest configuration of the OS
		 * Lock.
		 */
		} else if (kvm_vcpu_os_lock_enabled(vcpu)) {
			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
			mdscr &= ~DBG_MDSCR_MDE;
			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
		}
	}
}

void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
{
	/*
	 * Restore the guest's debug registers if we were using them.
	 */
	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
		if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
			if (!(*vcpu_cpsr(vcpu) & DBG_SPSR_SS))
				/*
				 * Mark the vcpu as ACTIVE_PENDING
				 * until Software Step exception is taken.
				 */
				vcpu_set_flag(vcpu, DBG_SS_ACTIVE_PENDING);
		}

		restore_guest_debug_regs(vcpu);
	}
}

void kvm_init_host_debug_data(void)
{
	u64 dfr0 = read_sysreg(id_aa64dfr0_el1);

	if (cpuid_feature_extract_signed_field(dfr0, ID_AA64DFR0_EL1_PMUVer_SHIFT) > 0)
		*host_data_ptr(nr_event_counters) = FIELD_GET(ARMV8_PMU_PMCR_N,
							      read_sysreg(pmcr_el0));

	if (has_vhe())
		return;

	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMSVer_SHIFT) &&
	    !(read_sysreg_s(SYS_PMBIDR_EL1) & PMBIDR_EL1_P))
		host_data_set_flag(HAS_SPE);

	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
	    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
		host_data_set_flag(HAS_TRBE);
}

void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
{
	u64 mdscr;

	/* Must be called before kvm_vcpu_load_vhe() */
	KVM_BUG_ON(vcpu_get_flag(vcpu, SYSREGS_ON_CPU), vcpu->kvm);

	/*
	 * Determine which of the possible debug states we're in:
	 *
	 *  - VCPU_DEBUG_HOST_OWNED: KVM has taken ownership of the guest's
	 *    breakpoint/watchpoint registers, or needs to use MDSCR_EL1 to do
	 *    software step or emulate the effects of the OS Lock being enabled.
	 *
	 *  - VCPU_DEBUG_GUEST_OWNED: The guest has debug exceptions enabled, and
	 *    the breakpoint/watchpoint registers need to be loaded eagerly.
	 *
	 *  - VCPU_DEBUG_FREE: Neither of the above apply, no breakpoint/watchpoint
	 *    context needs to be loaded on the CPU.
	 */
	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
		vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED;
	} else {
		mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

		if (mdscr & (MDSCR_EL1_KDE | MDSCR_EL1_MDE))
			vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
		else
			vcpu->arch.debug_owner = VCPU_DEBUG_FREE;
	}

	kvm_arm_setup_mdcr_el2(vcpu);
}

/*
 * Updates ownership of the debug registers after a trapped guest access to a
 * breakpoint/watchpoint register. Host ownership of the debug registers is of
 * strictly higher priority, and it is the responsibility of the VMM to emulate
 * guest debug exceptions in this configuration.
 */
void kvm_debug_set_guest_ownership(struct kvm_vcpu *vcpu)
{
	if (kvm_host_owns_debug_regs(vcpu))
		return;

	vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
	kvm_arm_setup_mdcr_el2(vcpu);
}

void kvm_debug_handle_oslar(struct kvm_vcpu *vcpu, u64 val)
{
	if (val & OSLAR_EL1_OSLK)
		__vcpu_sys_reg(vcpu, OSLSR_EL1) |= OSLSR_EL1_OSLK;
	else
		__vcpu_sys_reg(vcpu, OSLSR_EL1) &= ~OSLSR_EL1_OSLK;

	preempt_disable();
	kvm_arch_vcpu_put(vcpu);
	kvm_arch_vcpu_load(vcpu, smp_processor_id());
	preempt_enable();
}