MIPS: KVM: Add master disable count interface
Expose two new virtual registers to userland via the
KVM_{GET,SET}_ONE_REG ioctls.
KVM_REG_MIPS_COUNT_CTL is for timer configuration fields and just
contains a master disable count bit. This can be used by userland to
freeze the timer in order to read a consistent state from the timer
count value and timer interrupt pending bit. This cannot be done with
the CP0_Cause.DC bit because the timer interrupt pending bit (TI) is
also in CP0_Cause so it would be impossible to stop the timer without
also risking a race with an hrtimer interrupt and having to explicitly
check whether an interrupt should have occurred.
When the timer is re-enabled it resumes without losing time, i.e. the
CP0_Count value jumps to what it would have been had the timer not been
disabled, which would also be impossible to do from userland with
CP0_Cause.DC. The timer interrupt also cannot be lost, i.e. if a timer
interrupt would have occurred had the timer not been disabled it is
queued when the timer is re-enabled.
This works by storing the nanosecond monotonic time when the master
disable is set, and using it for various operations instead of the
current monotonic time (e.g. when recalculating the bias when the
CP0_Count is set), until the master disable is cleared again, i.e. the
timer state is read/written as it would have been at that time. This
state is exposed to userland via the read-only KVM_REG_MIPS_COUNT_RESUME
virtual register so that userland can determine the exact time the
master disable took effect.
This should allow userland to atomically save the state of the timer,
and later restore it.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: David Daney <david.daney@cavium.com>
Cc: Sanjay Lal <sanjayl@kymasys.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index 088c25d..65c8dea 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -233,14 +233,15 @@
* 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.
+ * Returns: 1 if the CP0_Count timer is disabled by either the guest
+ * CP0_Cause.DC bit or the count_ctl.DC bit.
* 0 otherwise (in which case CP0_Count timer is running).
*/
static inline int kvm_mips_count_disabled(struct kvm_vcpu *vcpu)
{
struct mips_coproc *cop0 = vcpu->arch.cop0;
- return kvm_read_c0_guest_cause(cop0) & CAUSEF_DC;
+ return (vcpu->arch.count_ctl & KVM_REG_MIPS_COUNT_CTL_DC) ||
+ (kvm_read_c0_guest_cause(cop0) & CAUSEF_DC);
}
/**
@@ -280,6 +281,24 @@
}
/**
+ * kvm_mips_count_time() - Get effective current time.
+ * @vcpu: Virtual CPU.
+ *
+ * Get effective monotonic ktime. This is usually a straightforward ktime_get(),
+ * except when the master disable bit is set in count_ctl, in which case it is
+ * count_resume, i.e. the time that the count was disabled.
+ *
+ * Returns: Effective monotonic ktime for CP0_Count.
+ */
+static inline ktime_t kvm_mips_count_time(struct kvm_vcpu *vcpu)
+{
+ if (unlikely(vcpu->arch.count_ctl & KVM_REG_MIPS_COUNT_CTL_DC))
+ return vcpu->arch.count_resume;
+
+ return ktime_get();
+}
+
+/**
* kvm_mips_read_count_running() - Read the current count value as if running.
* @vcpu: Virtual CPU.
* @now: Kernel time to read CP0_Count at.
@@ -448,7 +467,7 @@
ktime_t now;
/* Calculate bias */
- now = ktime_get();
+ now = kvm_mips_count_time(vcpu);
vcpu->arch.count_bias = count - kvm_mips_ktime_to_count(vcpu, now);
if (kvm_mips_count_disabled(vcpu))
@@ -508,8 +527,8 @@
* 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).
+ * Assumes CP0_Count was previously enabled but now Guest.CP0_Cause.DC or
+ * count_ctl.DC has been set (count disabled).
*
* Returns: The time that the timer was stopped.
*/
@@ -535,7 +554,8 @@
* @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.
+ * before the final stop time will be handled if the timer isn't disabled by
+ * count_ctl.DC, but not after.
*
* Assumes CP0_Cause.DC is clear (count enabled).
*/
@@ -544,7 +564,8 @@
struct mips_coproc *cop0 = vcpu->arch.cop0;
kvm_set_c0_guest_cause(cop0, CAUSEF_DC);
- kvm_mips_count_disable(vcpu);
+ if (!(vcpu->arch.count_ctl & KVM_REG_MIPS_COUNT_CTL_DC))
+ kvm_mips_count_disable(vcpu);
}
/**
@@ -552,9 +573,9 @@
* @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.
+ * the start time will be handled if the timer isn't disabled by count_ctl.DC,
+ * 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).
*/
@@ -567,13 +588,100 @@
/*
* Set the dynamic count to match the static count.
- * This starts the hrtimer.
+ * This starts the hrtimer if count_ctl.DC allows it.
+ * Otherwise it conveniently updates the biases.
*/
count = kvm_read_c0_guest_count(cop0);
kvm_mips_write_count(vcpu, count);
}
/**
+ * kvm_mips_set_count_ctl() - Update the count control KVM register.
+ * @vcpu: Virtual CPU.
+ * @count_ctl: Count control register new value.
+ *
+ * Set the count control KVM register. The timer is updated accordingly.
+ *
+ * Returns: -EINVAL if reserved bits are set.
+ * 0 on success.
+ */
+int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl)
+{
+ struct mips_coproc *cop0 = vcpu->arch.cop0;
+ s64 changed = count_ctl ^ vcpu->arch.count_ctl;
+ s64 delta;
+ ktime_t expire, now;
+ uint32_t count, compare;
+
+ /* Only allow defined bits to be changed */
+ if (changed & ~(s64)(KVM_REG_MIPS_COUNT_CTL_DC))
+ return -EINVAL;
+
+ /* Apply new value */
+ vcpu->arch.count_ctl = count_ctl;
+
+ /* Master CP0_Count disable */
+ if (changed & KVM_REG_MIPS_COUNT_CTL_DC) {
+ /* Is CP0_Cause.DC already disabling CP0_Count? */
+ if (kvm_read_c0_guest_cause(cop0) & CAUSEF_DC) {
+ if (count_ctl & KVM_REG_MIPS_COUNT_CTL_DC)
+ /* Just record the current time */
+ vcpu->arch.count_resume = ktime_get();
+ } else if (count_ctl & KVM_REG_MIPS_COUNT_CTL_DC) {
+ /* disable timer and record current time */
+ vcpu->arch.count_resume = kvm_mips_count_disable(vcpu);
+ } else {
+ /*
+ * Calculate timeout relative to static count at resume
+ * time (wrap 0 to 2^32).
+ */
+ count = kvm_read_c0_guest_count(cop0);
+ 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(vcpu->arch.count_resume, delta);
+
+ /* Handle pending interrupt */
+ now = ktime_get();
+ if (ktime_compare(now, expire) >= 0)
+ /* Nothing should be waiting on the timeout */
+ kvm_mips_callbacks->queue_timer_int(vcpu);
+
+ /* Resume hrtimer without changing bias */
+ count = kvm_mips_read_count_running(vcpu, now);
+ kvm_mips_resume_hrtimer(vcpu, now, count);
+ }
+ }
+
+ return 0;
+}
+
+/**
+ * kvm_mips_set_count_resume() - Update the count resume KVM register.
+ * @vcpu: Virtual CPU.
+ * @count_resume: Count resume register new value.
+ *
+ * Set the count resume KVM register.
+ *
+ * Returns: -EINVAL if out of valid range (0..now).
+ * 0 on success.
+ */
+int kvm_mips_set_count_resume(struct kvm_vcpu *vcpu, s64 count_resume)
+{
+ /*
+ * It doesn't make sense for the resume time to be in the future, as it
+ * would be possible for the next interrupt to be more than a full
+ * period in the future.
+ */
+ if (count_resume < 0 || count_resume > ktime_to_ns(ktime_get()))
+ return -EINVAL;
+
+ vcpu->arch.count_resume = ns_to_ktime(count_resume);
+ return 0;
+}
+
+/**
* kvm_mips_count_timeout() - Push timer forward on timeout.
* @vcpu: Virtual CPU.
*