From e30492bbe95a2495930aa7db7eacde5141e45332 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Thu, 29 May 2014 10:16:35 +0100 Subject: [PATCH] MIPS: KVM: Rewrite count/compare timer emulation Previously the emulation of the CPU timer was just enough to get a Linux guest running but some shortcuts were taken: - The guest timer interrupt was hard coded to always happen every 10 ms rather than being timed to when CP0_Count would match CP0_Compare. - The guest's CP0_Count register was based on the host's CP0_Count register. This isn't very portable and fails on cores without a CP_Count register implemented such as Ingenic XBurst. It also meant that the guest's CP0_Cause.DC bit to disable the CP0_Count register took no effect. - The guest's CP0_Count register was emulated by just dividing the host's CP0_Count register by 4. This resulted in continuity problems when used as a clock source, since when the host CP0_Count overflows from 0x7fffffff to 0x80000000, the guest CP0_Count transitions discontinuously from 0x1fffffff to 0xe0000000. Therefore rewrite & fix emulation of the guest timer based on the monotonic kernel time (i.e. ktime_get()). Internally a 32-bit count_bias value is added to the frequency scaled nanosecond monotonic time to get the guest's CP0_Count. The frequency of the timer is initialised to 100MHz and cannot yet be changed, but a later patch will allow the frequency to be configured via the KVM_{GET,SET}_ONE_REG ioctl interface. The timer can now be stopped via the CP0_Cause.DC bit (by the guest or via the KVM_SET_ONE_REG ioctl interface), at which point the current CP0_Count is stored and can be read directly. When it is restarted the bias is recalculated such that the CP0_Count value is continuous. Due to the nature of hrtimer interrupts any read of the guest's CP0_Count register while it is running triggers a check for whether the hrtimer has expired, so that the guest/userland cannot observe the CP0_Count passing CP0_Compare without queuing a timer interrupt. This is also taken advantage of when stopping the timer to ensure that a pending timer interrupt is queued. This replaces the implementation of: - Guest read of CP0_Count - Guest write of CP0_Count - Guest write of CP0_Compare - Guest write of CP0_Cause - Guest read of HWR 2 (CC) with RDHWR - Host read of CP0_Count via KVM_GET_ONE_REG ioctl interface - Host write of CP0_Count via KVM_SET_ONE_REG ioctl interface - Host write of CP0_Compare via KVM_SET_ONE_REG ioctl interface - Host write of CP0_Cause via KVM_SET_ONE_REG ioctl interface Signed-off-by: James Hogan Cc: Paolo Bonzini Cc: Gleb Natapov Cc: kvm@vger.kernel.org Cc: Ralf Baechle Cc: linux-mips@linux-mips.org Cc: Sanjay Lal Signed-off-by: Paolo Bonzini --- arch/mips/include/asm/kvm_host.h | 21 +- arch/mips/kvm/kvm_mips.c | 10 +- arch/mips/kvm/kvm_mips_emul.c | 393 +++++++++++++++++++++++++++++-- arch/mips/kvm/kvm_trap_emul.c | 27 ++- 4 files changed, 413 insertions(+), 38 deletions(-) diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h index 79410f85a5a7..75ed94aeefe7 100644 --- a/arch/mips/include/asm/kvm_host.h +++ b/arch/mips/include/asm/kvm_host.h @@ -404,8 +404,15 @@ struct kvm_vcpu_arch { u32 io_gpr; /* GPR used as IO source/target */ - /* Used to calibrate the virutal count register for the guest */ - int32_t host_cp0_count; + struct hrtimer comparecount_timer; + /* Count bias from the raw time */ + uint32_t count_bias; + /* Frequency of timer in Hz */ + uint32_t count_hz; + /* Dynamic nanosecond bias (multiple of count_period) to avoid overflow */ + s64 count_dyn_bias; + /* Period of timer tick in ns */ + u64 count_period; /* Bitmask of exceptions that are pending */ unsigned long pending_exceptions; @@ -426,8 +433,6 @@ struct kvm_vcpu_arch { uint32_t guest_kernel_asid[NR_CPUS]; struct mm_struct guest_kernel_mm, guest_user_mm; - struct hrtimer comparecount_timer; - int last_sched_cpu; /* WAIT executed */ @@ -705,7 +710,13 @@ extern enum emulation_result kvm_mips_emulate_bp_exc(unsigned long cause, extern enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run); -enum emulation_result kvm_mips_emulate_count(struct kvm_vcpu *vcpu); +uint32_t kvm_mips_read_count(struct kvm_vcpu *vcpu); +void kvm_mips_write_count(struct kvm_vcpu *vcpu, uint32_t count); +void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare); +void kvm_mips_init_count(struct kvm_vcpu *vcpu); +void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu); +void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu); +enum hrtimer_restart kvm_mips_count_timeout(struct kvm_vcpu *vcpu); enum emulation_result kvm_mips_check_privilege(unsigned long cause, uint32_t *opc, diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c index 0a9c7ab56df1..fc5e44d827fc 100644 --- a/arch/mips/kvm/kvm_mips.c +++ b/arch/mips/kvm/kvm_mips.c @@ -363,7 +363,7 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id) vcpu->arch.last_sched_cpu = -1; /* Start off the timer */ - kvm_mips_emulate_count(vcpu); + kvm_mips_init_count(vcpu); return vcpu; @@ -707,9 +707,6 @@ static int kvm_mips_set_reg(struct kvm_vcpu *vcpu, case KVM_REG_MIPS_CP0_STATUS: kvm_write_c0_guest_status(cop0, v); break; - case KVM_REG_MIPS_CP0_CAUSE: - kvm_write_c0_guest_cause(cop0, v); - break; case KVM_REG_MIPS_CP0_EPC: kvm_write_c0_guest_epc(cop0, v); break; @@ -719,6 +716,7 @@ static int kvm_mips_set_reg(struct kvm_vcpu *vcpu, /* registers to be handled specially */ case KVM_REG_MIPS_CP0_COUNT: case KVM_REG_MIPS_CP0_COMPARE: + case KVM_REG_MIPS_CP0_CAUSE: return kvm_mips_callbacks->set_one_reg(vcpu, reg, v); default: return -EINVAL; @@ -992,9 +990,7 @@ enum hrtimer_restart kvm_mips_comparecount_wakeup(struct hrtimer *timer) vcpu = container_of(timer, struct kvm_vcpu, arch.comparecount_timer); kvm_mips_comparecount_func((unsigned long) vcpu); - hrtimer_forward_now(&vcpu->arch.comparecount_timer, - ktime_set(0, MS_TO_NS(10))); - return HRTIMER_RESTART; + return kvm_mips_count_timeout(vcpu); } int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c index bad31c6235d4..088c25d73a11 100644 --- a/arch/mips/kvm/kvm_mips_emul.c +++ b/arch/mips/kvm/kvm_mips_emul.c @@ -11,6 +11,7 @@ #include #include +#include #include #include #include @@ -228,25 +229,364 @@ enum emulation_result update_pc(struct kvm_vcpu *vcpu, uint32_t cause) return er; } -/* Everytime the compare register is written to, we need to decide when to fire - * the timer that represents timer ticks to the GUEST. +/** + * kvm_mips_count_disabled() - Find whether the CP0_Count timer is disabled. + * @vcpu: Virtual CPU. * + * Returns: 1 if the CP0_Count timer is disabled by the guest CP0_Cause.DC + * bit. + * 0 otherwise (in which case CP0_Count timer is running). */ -enum emulation_result kvm_mips_emulate_count(struct kvm_vcpu *vcpu) +static inline int kvm_mips_count_disabled(struct kvm_vcpu *vcpu) { struct mips_coproc *cop0 = vcpu->arch.cop0; - enum emulation_result er = EMULATE_DONE; + return kvm_read_c0_guest_cause(cop0) & CAUSEF_DC; +} - /* If COUNT is enabled */ - if (!(kvm_read_c0_guest_cause(cop0) & CAUSEF_DC)) { - hrtimer_try_to_cancel(&vcpu->arch.comparecount_timer); - hrtimer_start(&vcpu->arch.comparecount_timer, - ktime_set(0, MS_TO_NS(10)), HRTIMER_MODE_REL); - } else { - hrtimer_try_to_cancel(&vcpu->arch.comparecount_timer); +/** + * kvm_mips_ktime_to_count() - Scale ktime_t to a 32-bit count. + * + * Caches the dynamic nanosecond bias in vcpu->arch.count_dyn_bias. + * + * Assumes !kvm_mips_count_disabled(@vcpu) (guest CP0_Count timer is running). + */ +static uint32_t kvm_mips_ktime_to_count(struct kvm_vcpu *vcpu, ktime_t now) +{ + s64 now_ns, periods; + u64 delta; + + now_ns = ktime_to_ns(now); + delta = now_ns + vcpu->arch.count_dyn_bias; + + if (delta >= vcpu->arch.count_period) { + /* If delta is out of safe range the bias needs adjusting */ + periods = div64_s64(now_ns, vcpu->arch.count_period); + vcpu->arch.count_dyn_bias = -periods * vcpu->arch.count_period; + /* Recalculate delta with new bias */ + delta = now_ns + vcpu->arch.count_dyn_bias; } - return er; + /* + * We've ensured that: + * delta < count_period + * + * Therefore the intermediate delta*count_hz will never overflow since + * at the boundary condition: + * delta = count_period + * delta = NSEC_PER_SEC * 2^32 / count_hz + * delta * count_hz = NSEC_PER_SEC * 2^32 + */ + return div_u64(delta * vcpu->arch.count_hz, NSEC_PER_SEC); +} + +/** + * kvm_mips_read_count_running() - Read the current count value as if running. + * @vcpu: Virtual CPU. + * @now: Kernel time to read CP0_Count at. + * + * Returns the current guest CP0_Count register at time @now and handles if the + * timer interrupt is pending and hasn't been handled yet. + * + * Returns: The current value of the guest CP0_Count register. + */ +static uint32_t kvm_mips_read_count_running(struct kvm_vcpu *vcpu, ktime_t now) +{ + ktime_t expires; + int running; + + /* Is the hrtimer pending? */ + expires = hrtimer_get_expires(&vcpu->arch.comparecount_timer); + if (ktime_compare(now, expires) >= 0) { + /* + * Cancel it while we handle it so there's no chance of + * interference with the timeout handler. + */ + running = hrtimer_cancel(&vcpu->arch.comparecount_timer); + + /* Nothing should be waiting on the timeout */ + kvm_mips_callbacks->queue_timer_int(vcpu); + + /* + * Restart the timer if it was running based on the expiry time + * we read, so that we don't push it back 2 periods. + */ + if (running) { + expires = ktime_add_ns(expires, + vcpu->arch.count_period); + hrtimer_start(&vcpu->arch.comparecount_timer, expires, + HRTIMER_MODE_ABS); + } + } + + /* Return the biased and scaled guest CP0_Count */ + return vcpu->arch.count_bias + kvm_mips_ktime_to_count(vcpu, now); +} + +/** + * kvm_mips_read_count() - Read the current count value. + * @vcpu: Virtual CPU. + * + * Read the current guest CP0_Count value, taking into account whether the timer + * is stopped. + * + * Returns: The current guest CP0_Count value. + */ +uint32_t kvm_mips_read_count(struct kvm_vcpu *vcpu) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + + /* If count disabled just read static copy of count */ + if (kvm_mips_count_disabled(vcpu)) + return kvm_read_c0_guest_count(cop0); + + return kvm_mips_read_count_running(vcpu, ktime_get()); +} + +/** + * kvm_mips_freeze_hrtimer() - Safely stop the hrtimer. + * @vcpu: Virtual CPU. + * @count: Output pointer for CP0_Count value at point of freeze. + * + * Freeze the hrtimer safely and return both the ktime and the CP0_Count value + * at the point it was frozen. It is guaranteed that any pending interrupts at + * the point it was frozen are handled, and none after that point. + * + * This is useful where the time/CP0_Count is needed in the calculation of the + * new parameters. + * + * Assumes !kvm_mips_count_disabled(@vcpu) (guest CP0_Count timer is running). + * + * Returns: The ktime at the point of freeze. + */ +static ktime_t kvm_mips_freeze_hrtimer(struct kvm_vcpu *vcpu, + uint32_t *count) +{ + ktime_t now; + + /* stop hrtimer before finding time */ + hrtimer_cancel(&vcpu->arch.comparecount_timer); + now = ktime_get(); + + /* find count at this point and handle pending hrtimer */ + *count = kvm_mips_read_count_running(vcpu, now); + + return now; +} + + +/** + * kvm_mips_resume_hrtimer() - Resume hrtimer, updating expiry. + * @vcpu: Virtual CPU. + * @now: ktime at point of resume. + * @count: CP0_Count at point of resume. + * + * Resumes the timer and updates the timer expiry based on @now and @count. + * This can be used in conjunction with kvm_mips_freeze_timer() when timer + * parameters need to be changed. + * + * It is guaranteed that a timer interrupt immediately after resume will be + * handled, but not if CP_Compare is exactly at @count. That case is already + * handled by kvm_mips_freeze_timer(). + * + * Assumes !kvm_mips_count_disabled(@vcpu) (guest CP0_Count timer is running). + */ +static void kvm_mips_resume_hrtimer(struct kvm_vcpu *vcpu, + ktime_t now, uint32_t count) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + uint32_t compare; + u64 delta; + ktime_t expire; + + /* Calculate timeout (wrap 0 to 2^32) */ + compare = kvm_read_c0_guest_compare(cop0); + delta = (u64)(uint32_t)(compare - count - 1) + 1; + delta = div_u64(delta * NSEC_PER_SEC, vcpu->arch.count_hz); + expire = ktime_add_ns(now, delta); + + /* Update hrtimer to use new timeout */ + hrtimer_cancel(&vcpu->arch.comparecount_timer); + hrtimer_start(&vcpu->arch.comparecount_timer, expire, HRTIMER_MODE_ABS); +} + +/** + * kvm_mips_update_hrtimer() - Update next expiry time of hrtimer. + * @vcpu: Virtual CPU. + * + * Recalculates and updates the expiry time of the hrtimer. This can be used + * after timer parameters have been altered which do not depend on the time that + * the change occurs (in those cases kvm_mips_freeze_hrtimer() and + * kvm_mips_resume_hrtimer() are used directly). + * + * It is guaranteed that no timer interrupts will be lost in the process. + * + * Assumes !kvm_mips_count_disabled(@vcpu) (guest CP0_Count timer is running). + */ +static void kvm_mips_update_hrtimer(struct kvm_vcpu *vcpu) +{ + ktime_t now; + uint32_t count; + + /* + * freeze_hrtimer takes care of a timer interrupts <= count, and + * resume_hrtimer the hrtimer takes care of a timer interrupts > count. + */ + now = kvm_mips_freeze_hrtimer(vcpu, &count); + kvm_mips_resume_hrtimer(vcpu, now, count); +} + +/** + * kvm_mips_write_count() - Modify the count and update timer. + * @vcpu: Virtual CPU. + * @count: Guest CP0_Count value to set. + * + * Sets the CP0_Count value and updates the timer accordingly. + */ +void kvm_mips_write_count(struct kvm_vcpu *vcpu, uint32_t count) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + ktime_t now; + + /* Calculate bias */ + now = ktime_get(); + vcpu->arch.count_bias = count - kvm_mips_ktime_to_count(vcpu, now); + + if (kvm_mips_count_disabled(vcpu)) + /* The timer's disabled, adjust the static count */ + kvm_write_c0_guest_count(cop0, count); + else + /* Update timeout */ + kvm_mips_resume_hrtimer(vcpu, now, count); +} + +/** + * kvm_mips_init_count() - Initialise timer. + * @vcpu: Virtual CPU. + * + * Initialise the timer to a sensible frequency, namely 100MHz, zero it, and set + * it going if it's enabled. + */ +void kvm_mips_init_count(struct kvm_vcpu *vcpu) +{ + /* 100 MHz */ + vcpu->arch.count_hz = 100*1000*1000; + vcpu->arch.count_period = div_u64((u64)NSEC_PER_SEC << 32, + vcpu->arch.count_hz); + vcpu->arch.count_dyn_bias = 0; + + /* Starting at 0 */ + kvm_mips_write_count(vcpu, 0); +} + +/** + * kvm_mips_write_compare() - Modify compare and update timer. + * @vcpu: Virtual CPU. + * @compare: New CP0_Compare value. + * + * Update CP0_Compare to a new value and update the timeout. + */ +void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + + /* if unchanged, must just be an ack */ + if (kvm_read_c0_guest_compare(cop0) == compare) + return; + + /* Update compare */ + kvm_write_c0_guest_compare(cop0, compare); + + /* Update timeout if count enabled */ + if (!kvm_mips_count_disabled(vcpu)) + kvm_mips_update_hrtimer(vcpu); +} + +/** + * kvm_mips_count_disable() - Disable count. + * @vcpu: Virtual CPU. + * + * Disable the CP0_Count timer. A timer interrupt on or before the final stop + * time will be handled but not after. + * + * Assumes CP0_Count was previously enabled but now Guest.CP0_Cause.DC has been + * set (count disabled). + * + * Returns: The time that the timer was stopped. + */ +static ktime_t kvm_mips_count_disable(struct kvm_vcpu *vcpu) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + uint32_t count; + ktime_t now; + + /* Stop hrtimer */ + hrtimer_cancel(&vcpu->arch.comparecount_timer); + + /* Set the static count from the dynamic count, handling pending TI */ + now = ktime_get(); + count = kvm_mips_read_count_running(vcpu, now); + kvm_write_c0_guest_count(cop0, count); + + return now; +} + +/** + * kvm_mips_count_disable_cause() - Disable count using CP0_Cause.DC. + * @vcpu: Virtual CPU. + * + * Disable the CP0_Count timer and set CP0_Cause.DC. A timer interrupt on or + * before the final stop time will be handled, but not after. + * + * Assumes CP0_Cause.DC is clear (count enabled). + */ +void kvm_mips_count_disable_cause(struct kvm_vcpu *vcpu) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + + kvm_set_c0_guest_cause(cop0, CAUSEF_DC); + kvm_mips_count_disable(vcpu); +} + +/** + * kvm_mips_count_enable_cause() - Enable count using CP0_Cause.DC. + * @vcpu: Virtual CPU. + * + * Enable the CP0_Count timer and clear CP0_Cause.DC. A timer interrupt after + * the start time will be handled, potentially before even returning, so the + * caller should be careful with ordering of CP0_Cause modifications so as not + * to lose it. + * + * Assumes CP0_Cause.DC is set (count disabled). + */ +void kvm_mips_count_enable_cause(struct kvm_vcpu *vcpu) +{ + struct mips_coproc *cop0 = vcpu->arch.cop0; + uint32_t count; + + kvm_clear_c0_guest_cause(cop0, CAUSEF_DC); + + /* + * Set the dynamic count to match the static count. + * This starts the hrtimer. + */ + count = kvm_read_c0_guest_count(cop0); + kvm_mips_write_count(vcpu, count); +} + +/** + * kvm_mips_count_timeout() - Push timer forward on timeout. + * @vcpu: Virtual CPU. + * + * Handle an hrtimer event by push the hrtimer forward a period. + * + * Returns: The hrtimer_restart value to return to the hrtimer subsystem. + */ +enum hrtimer_restart kvm_mips_count_timeout(struct kvm_vcpu *vcpu) +{ + /* Add the Count period to the current expiry time */ + hrtimer_add_expires_ns(&vcpu->arch.comparecount_timer, + vcpu->arch.count_period); + return HRTIMER_RESTART; } enum emulation_result kvm_mips_emul_eret(struct kvm_vcpu *vcpu) @@ -471,8 +811,7 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause, #endif /* Get reg */ if ((rd == MIPS_CP0_COUNT) && (sel == 0)) { - /* XXXKYMA: Run the Guest count register @ 1/4 the rate of the host */ - vcpu->arch.gprs[rt] = (read_c0_count() >> 2); + vcpu->arch.gprs[rt] = kvm_mips_read_count(vcpu); } else if ((rd == MIPS_CP0_ERRCTL) && (sel == 0)) { vcpu->arch.gprs[rt] = 0x0; #ifdef CONFIG_KVM_MIPS_DYN_TRANS @@ -539,10 +878,7 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause, } /* Are we writing to COUNT */ else if ((rd == MIPS_CP0_COUNT) && (sel == 0)) { - /* Linux doesn't seem to write into COUNT, we throw an error - * if we notice a write to COUNT - */ - /*er = EMULATE_FAIL; */ + kvm_mips_write_count(vcpu, vcpu->arch.gprs[rt]); goto done; } else if ((rd == MIPS_CP0_COMPARE) && (sel == 0)) { kvm_debug("[%#x] MTCz, COMPARE %#lx <- %#lx\n", @@ -552,8 +888,8 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause, /* If we are writing to COMPARE */ /* Clear pending timer interrupt, if any */ kvm_mips_callbacks->dequeue_timer_int(vcpu); - kvm_write_c0_guest_compare(cop0, - vcpu->arch.gprs[rt]); + kvm_mips_write_compare(vcpu, + vcpu->arch.gprs[rt]); } else if ((rd == MIPS_CP0_STATUS) && (sel == 0)) { kvm_write_c0_guest_status(cop0, vcpu->arch.gprs[rt]); @@ -564,6 +900,20 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause, #ifdef CONFIG_KVM_MIPS_DYN_TRANS kvm_mips_trans_mtc0(inst, opc, vcpu); #endif + } else if ((rd == MIPS_CP0_CAUSE) && (sel == 0)) { + uint32_t old_cause, new_cause; + old_cause = kvm_read_c0_guest_cause(cop0); + new_cause = vcpu->arch.gprs[rt]; + /* Update R/W bits */ + kvm_change_c0_guest_cause(cop0, 0x08800300, + new_cause); + /* DC bit enabling/disabling timer? */ + if ((old_cause ^ new_cause) & CAUSEF_DC) { + if (new_cause & CAUSEF_DC) + kvm_mips_count_disable_cause(vcpu); + else + kvm_mips_count_enable_cause(vcpu); + } } else { cop0->reg[rd][sel] = vcpu->arch.gprs[rt]; #ifdef CONFIG_KVM_MIPS_DYN_TRANS @@ -1553,8 +1903,7 @@ kvm_mips_handle_ri(unsigned long cause, uint32_t *opc, current_cpu_data.icache.linesz); break; case 2: /* Read count register */ - printk("RDHWR: Cont register\n"); - arch->gprs[rt] = kvm_read_c0_guest_count(cop0); + arch->gprs[rt] = kvm_mips_read_count(vcpu); break; case 3: /* Count register resolution */ switch (current_cpu_data.cputype) { diff --git a/arch/mips/kvm/kvm_trap_emul.c b/arch/mips/kvm/kvm_trap_emul.c index f1e8389f8d33..9908f2b0ff46 100644 --- a/arch/mips/kvm/kvm_trap_emul.c +++ b/arch/mips/kvm/kvm_trap_emul.c @@ -407,8 +407,7 @@ static int kvm_trap_emul_get_one_reg(struct kvm_vcpu *vcpu, { switch (reg->id) { case KVM_REG_MIPS_CP0_COUNT: - /* XXXKYMA: Run the Guest count register @ 1/4 the rate of the host */ - *v = (read_c0_count() >> 2); + *v = kvm_mips_read_count(vcpu); break; default: return -EINVAL; @@ -424,10 +423,30 @@ static int kvm_trap_emul_set_one_reg(struct kvm_vcpu *vcpu, switch (reg->id) { case KVM_REG_MIPS_CP0_COUNT: - /* Not supported yet */ + kvm_mips_write_count(vcpu, v); break; case KVM_REG_MIPS_CP0_COMPARE: - kvm_write_c0_guest_compare(cop0, v); + kvm_mips_write_compare(vcpu, v); + break; + case KVM_REG_MIPS_CP0_CAUSE: + /* + * If the timer is stopped or started (DC bit) it must look + * atomic with changes to the interrupt pending bits (TI, IRQ5). + * A timer interrupt should not happen in between. + */ + if ((kvm_read_c0_guest_cause(cop0) ^ v) & CAUSEF_DC) { + if (v & CAUSEF_DC) { + /* disable timer first */ + kvm_mips_count_disable_cause(vcpu); + kvm_change_c0_guest_cause(cop0, ~CAUSEF_DC, v); + } else { + /* enable timer last */ + kvm_change_c0_guest_cause(cop0, ~CAUSEF_DC, v); + kvm_mips_count_enable_cause(vcpu); + } + } else { + kvm_write_c0_guest_cause(cop0, v); + } break; default: return -EINVAL;