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/*
* Debug and Guest Debug support
*
* Copyright (C) 2015 - Linaro Ltd
* Author: Alex Bennée <alex.bennee@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#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>
#include "trace.h"
/* These are the bits of MDSCR_EL1 we may manipulate */
#define MDSCR_EL1_DEBUG_MASK (DBG_MDSCR_SS | \
DBG_MDSCR_KDE | \
DBG_MDSCR_MDE)
static DEFINE_PER_CPU(u32, mdcr_el2);
/**
* 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.
*/
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;
trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
vcpu->arch.guest_debug_preserved.mdscr_el1);
}
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);
trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
vcpu_read_sys_reg(vcpu, MDSCR_EL1));
}
/**
* kvm_arm_init_debug - grab what we need for debug
*
* Currently the sole task of this function is to retrieve the initial
* value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
* presumably been set-up by some knowledgeable bootcode.
*
* It is called once per-cpu during CPU hyp initialisation.
*/
void kvm_arm_init_debug(void)
{
__this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2));
}
/**
* kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
*/
void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
{
vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
}
/**
* 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. Currently this just 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)
*
* Additionally, KVM only traps guest accesses to the debug registers if
* the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
* flag on vcpu->arch.flags). 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)
{
bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
unsigned long mdscr;
trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
/*
* This also clears MDCR_EL2_E2PB_MASK to disable guest access
* to the profiling buffer.
*/
vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
MDCR_EL2_TPMS |
MDCR_EL2_TPMCR |
MDCR_EL2_TDRA |
MDCR_EL2_TDOSA);
/* Is Guest debugging in effect? */
if (vcpu->guest_debug) {
/* Route all software debug exceptions to EL2 */
vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
/* 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) {
*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);
}
trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
/*
* HW Breakpoints and watchpoints
*
* We simply switch the debug_ptr to point to our new
* external_debug_state which has been populated by the
* debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
* mechanism ensures the registers are updated on the
* world switch.
*/
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
/* Enable breakpoints/watchpoints */
mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
mdscr |= DBG_MDSCR_MDE;
vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
trap_debug = true;
trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
&vcpu->arch.debug_ptr->dbg_bcr[0],
&vcpu->arch.debug_ptr->dbg_bvr[0]);
trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
&vcpu->arch.debug_ptr->dbg_wcr[0],
&vcpu->arch.debug_ptr->dbg_wvr[0]);
}
}
BUG_ON(!vcpu->guest_debug &&
vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
/* Trap debug register access */
if (trap_debug)
vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
/* If KDE or MDE are set, perform a full save/restore cycle. */
if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
}
void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
{
trace_kvm_arm_clear_debug(vcpu->guest_debug);
if (vcpu->guest_debug) {
restore_guest_debug_regs(vcpu);
/*
* If we were using HW debug we need to restore the
* debug_ptr to the guest debug state.
*/
if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
kvm_arm_reset_debug_ptr(vcpu);
trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
&vcpu->arch.debug_ptr->dbg_bcr[0],
&vcpu->arch.debug_ptr->dbg_bvr[0]);
trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
&vcpu->arch.debug_ptr->dbg_wcr[0],
&vcpu->arch.debug_ptr->dbg_wvr[0]);
}
}
}
/*
* After successfully emulating an instruction, we might want to
* return to user space with a KVM_EXIT_DEBUG. We can only do this
* once the emulation is complete, though, so for userspace emulations
* we have to wait until we have re-entered KVM before calling this
* helper.
*
* Return true (and set exit_reason) to return to userspace or false
* if no further action is required.
*/
bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
run->exit_reason = KVM_EXIT_DEBUG;
run->debug.arch.hsr = ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT;
return true;
}
return false;
}
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