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>

5 files changed, 65 insertions, 0 deletions

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 1deeaecbe73e..f9c672f729ea 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -720,6 +720,7 @@ void kvm_mips_write_compare(struct kvm_vcpu *vcpu, uint32_t compare);
 void kvm_mips_init_count(struct kvm_vcpu *vcpu);
 int kvm_mips_set_count_ctl(struct kvm_vcpu *vcpu, s64 count_ctl);
 int kvm_mips_set_count_resume(struct kvm_vcpu *vcpu, s64 count_resume);
+int kvm_mips_set_count_hz(struct kvm_vcpu *vcpu, s64 count_hz);
 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);
diff --git a/arch/mips/include/uapi/asm/kvm.h b/arch/mips/include/uapi/asm/kvm.h
index f859fbada1f7..2c04b6d9ff85 100644
--- a/arch/mips/include/uapi/asm/kvm.h
+++ b/arch/mips/include/uapi/asm/kvm.h
@@ -133,6 +133,13 @@ struct kvm_fpu {
  */
 #define KVM_REG_MIPS_COUNT_RESUME       (KVM_REG_MIPS | KVM_REG_SIZE_U64 | \
                                          0x20000 | 1)
+/*
+ * CP0_Count rate in Hz
+ * Specifies the rate of the CP0_Count timer in Hz. Modifications occur without
+ * discontinuities in CP0_Count.
+ */
+#define KVM_REG_MIPS_COUNT_HZ           (KVM_REG_MIPS | KVM_REG_SIZE_U64 | \
+                                         0x20000 | 2)
 
 /*
  * KVM MIPS specific structures and definitions
diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c
index a2d5d4243f51..7ccb7a532c55 100644
--- a/arch/mips/kvm/kvm_mips.c
+++ b/arch/mips/kvm/kvm_mips.c
@@ -546,6 +546,7 @@ static u64 kvm_mips_get_one_regs[] = {
 
         KVM_REG_MIPS_COUNT_CTL,
         KVM_REG_MIPS_COUNT_RESUME,
+        KVM_REG_MIPS_COUNT_HZ,
 };
 
 static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
@@ -627,6 +628,7 @@ static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
         case KVM_REG_MIPS_CP0_COUNT:
         case KVM_REG_MIPS_COUNT_CTL:
         case KVM_REG_MIPS_COUNT_RESUME:
+        case KVM_REG_MIPS_COUNT_HZ:
                 ret = kvm_mips_callbacks->get_one_reg(vcpu, reg, &v);
                 if (ret)
                         return ret;
@@ -724,6 +726,7 @@ static int kvm_mips_set_reg(struct kvm_vcpu *vcpu,
         case KVM_REG_MIPS_CP0_CAUSE:
         case KVM_REG_MIPS_COUNT_CTL:
         case KVM_REG_MIPS_COUNT_RESUME:
+        case KVM_REG_MIPS_COUNT_HZ:
                 return kvm_mips_callbacks->set_one_reg(vcpu, reg, v);
         default:
                 return -EINVAL;
diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index 65c8dea6d1f5..6d257384c9b4 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -498,6 +498,54 @@ void kvm_mips_init_count(struct kvm_vcpu *vcpu)
 }
 
 /**
+ * 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.
diff --git a/arch/mips/kvm/kvm_trap_emul.c b/arch/mips/kvm/kvm_trap_emul.c
index 854502bcc749..b171db324cf0 100644
--- a/arch/mips/kvm/kvm_trap_emul.c
+++ b/arch/mips/kvm/kvm_trap_emul.c
@@ -415,6 +415,9 @@ static int kvm_trap_emul_get_one_reg(struct kvm_vcpu *vcpu,
         case KVM_REG_MIPS_COUNT_RESUME:
                 *v = ktime_to_ns(vcpu->arch.count_resume);
                 break;
+        case KVM_REG_MIPS_COUNT_HZ:
+                *v = vcpu->arch.count_hz;
+                break;
         default:
                 return -EINVAL;
         }
@@ -461,6 +464,9 @@ static int kvm_trap_emul_set_one_reg(struct kvm_vcpu *vcpu,
         case KVM_REG_MIPS_COUNT_RESUME:
                 ret = kvm_mips_set_count_resume(vcpu, v);
                 break;
+        case KVM_REG_MIPS_COUNT_HZ:
+                ret = kvm_mips_set_count_hz(vcpu, v);
+                break;
         default:
                 return -EINVAL;
         }