MIPS: KVM: Add count frequency KVM register
Expose the KVM guest CP0_Count frequency to userland via a new
KVM_REG_MIPS_COUNT_HZ register accessible with the KVM_{GET,SET}_ONE_REG
ioctls.
When the frequency is altered the bias is adjusted such that the guest
CP0_Count doesn't jump discontinuously or lose any timer interrupts.
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 65c8dea..6d25738 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -498,6 +498,54 @@
}
/**
+ * kvm_mips_set_count_hz() - Update the frequency of the timer.
+ * @vcpu: Virtual CPU.
+ * @count_hz: Frequency of CP0_Count timer in Hz.
+ *
+ * Change the frequency of the CP0_Count timer. This is done atomically so that
+ * CP0_Count is continuous and no timer interrupt is lost.
+ *
+ * Returns: -EINVAL if @count_hz is out of range.
+ * 0 on success.
+ */
+int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz)
+{
+ struct mips_coproc *cop0 = vcpu->arch.cop0;
+ int dc;
+ ktime_t now;
+ u32 count;
+
+ /* ensure the frequency is in a sensible range... */
+ if (count_hz <= 0 || count_hz > NSEC_PER_SEC)
+ return -EINVAL;
+ /* ... and has actually changed */
+ if (vcpu->arch.count_hz == count_hz)
+ return 0;
+
+ /* Safely freeze timer so we can keep it continuous */
+ dc = kvm_mips_count_disabled(vcpu);
+ if (dc) {
+ now = kvm_mips_count_time(vcpu);
+ count = kvm_read_c0_guest_count(cop0);
+ } else {
+ now = kvm_mips_freeze_hrtimer(vcpu, &count);
+ }
+
+ /* Update the frequency */
+ vcpu->arch.count_hz = count_hz;
+ vcpu->arch.count_period = div_u64((u64)NSEC_PER_SEC << 32, count_hz);
+ vcpu->arch.count_dyn_bias = 0;
+
+ /* Calculate adjusted bias so dynamic count is unchanged */
+ vcpu->arch.count_bias = count - kvm_mips_ktime_to_count(vcpu, now);
+
+ /* Update and resume hrtimer */
+ if (!dc)
+ kvm_mips_resume_hrtimer(vcpu, now, count);
+ return 0;
+}
+
+/**
* kvm_mips_write_compare() - Modify compare and update timer.
* @vcpu: Virtual CPU.
* @compare: New CP0_Compare value.