[PATCH v4 6/7] mips/kvm: Support FPU in MIPS KVM guests

[James Hogan <james.hogan@imgtec.com>]

Support the new KVM_CAP_MIPS_FPU capability, which allows the host's FPU
to be exposed to the KVM guest.

The capability is enabled if the guest core has an FPU according to its
Config1 register. Various config bits are now writeable so that KVM is
aware of the configuration (Config1.FP) and so that QEMU can
save/restore the guest modifiable bits (Config5.FRE, Config5.UFR,
Config5.UFE). The FCSR/FIR registers and the floating point registers
are now saved/restored (depending on the FR mode bit).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Leon Alrae <leon.alrae@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
---
Changes in v2:
- Change (1 << x) to (1U << x) in important places to avoid compiler
  undefined behaviour (Leon).
- Removed update of linux-headers/linux/kvm.h (Paolo).
---
 target-mips/kvm.c | 124 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 120 insertions(+), 4 deletions(-)

diff --git a/target-mips/kvm.c b/target-mips/kvm.c
index 284b7a954ba2..f66347b8250a 100644
--- a/target-mips/kvm.c
+++ b/target-mips/kvm.c
@@ -30,6 +30,8 @@
 #define DPRINTF(fmt, ...) \
     do { if (DEBUG_KVM) { fprintf(stderr, fmt, ## __VA_ARGS__); } } while (0)
 
+static int kvm_mips_fpu_cap;
+
 const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
     KVM_CAP_LAST_INFO
 };
@@ -46,16 +48,29 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     /* MIPS has 128 signals */
     kvm_set_sigmask_len(s, 16);
 
+    kvm_mips_fpu_cap = kvm_check_extension(s, KVM_CAP_MIPS_FPU);
+
     DPRINTF("%s\n", __func__);
     return 0;
 }
 
 int kvm_arch_init_vcpu(CPUState *cs)
 {
+    MIPSCPU *cpu = MIPS_CPU(cs);
+    CPUMIPSState *env = &cpu->env;
     int ret = 0;
 
     qemu_add_vm_change_state_handler(kvm_mips_update_state, cs);
 
+    if (kvm_mips_fpu_cap && env->CP0_Config1 & (1 << CP0C1_FP)) {
+        ret = kvm_vcpu_enable_cap(cs, KVM_CAP_MIPS_FPU, 0, 0);
+        if (ret < 0) {
+            /* mark unsupported so it gets disabled on reset */
+            kvm_mips_fpu_cap = 0;
+            ret = 0;
+        }
+    }
+
     DPRINTF("%s\n", __func__);
     return ret;
 }
@@ -64,8 +79,8 @@ void kvm_mips_reset_vcpu(MIPSCPU *cpu)
 {
     CPUMIPSState *env = &cpu->env;
 
-    if (env->CP0_Config1 & (1 << CP0C1_FP)) {
-        fprintf(stderr, "Warning: FPU not supported with KVM, disabling\n");
+    if (!kvm_mips_fpu_cap && env->CP0_Config1 & (1 << CP0C1_FP)) {
+        fprintf(stderr, "Warning: KVM does not support FPU, disabling\n");
         env->CP0_Config1 &= ~(1 << CP0C1_FP);
     }
 
@@ -355,11 +370,14 @@ static inline int kvm_mips_get_one_ureg64(CPUState *cs, uint64 reg_id,
 }
 
 #define KVM_REG_MIPS_CP0_CONFIG_MASK    (1U << CP0C0_M)
-#define KVM_REG_MIPS_CP0_CONFIG1_MASK   (1U << CP0C1_M)
+#define KVM_REG_MIPS_CP0_CONFIG1_MASK   ((1U << CP0C1_M) | \
+                                         (1U << CP0C1_FP))
 #define KVM_REG_MIPS_CP0_CONFIG2_MASK   (1U << CP0C2_M)
 #define KVM_REG_MIPS_CP0_CONFIG3_MASK   (1U << CP0C3_M)
 #define KVM_REG_MIPS_CP0_CONFIG4_MASK   (1U << CP0C4_M)
-#define KVM_REG_MIPS_CP0_CONFIG5_MASK   0
+#define KVM_REG_MIPS_CP0_CONFIG5_MASK   ((1U << CP0C5_UFE) | \
+                                         (1U << CP0C5_FRE) | \
+                                         (1U << CP0C5_UFR))
 
 static inline int kvm_mips_change_one_reg(CPUState *cs, uint64_t reg_id,
                                           int32_t *addr, int32_t mask)
@@ -521,6 +539,98 @@ static void kvm_mips_update_state(void *opaque, int running, RunState state)
     }
 }
 
+static int kvm_mips_put_fpu_registers(CPUState *cs, int level)
+{
+    MIPSCPU *cpu = MIPS_CPU(cs);
+    CPUMIPSState *env = &cpu->env;
+    int err, ret = 0;
+    unsigned int i;
+
+    /* Only put FPU state if we're emulating a CPU with an FPU */
+    if (env->CP0_Config1 & (1 << CP0C1_FP)) {
+        /* FPU Control Registers */
+        if (level == KVM_PUT_FULL_STATE) {
+            err = kvm_mips_put_one_ureg(cs, KVM_REG_MIPS_FCR_IR,
+                                        &env->active_fpu.fcr0);
+            if (err < 0) {
+                DPRINTF("%s: Failed to put FCR_IR (%d)\n", __func__, err);
+                ret = err;
+            }
+        }
+        err = kvm_mips_put_one_ureg(cs, KVM_REG_MIPS_FCR_CSR,
+                                    &env->active_fpu.fcr31);
+        if (err < 0) {
+            DPRINTF("%s: Failed to put FCR_CSR (%d)\n", __func__, err);
+            ret = err;
+        }
+
+        /* Floating point registers */
+        for (i = 0; i < 32; ++i) {
+            if (env->CP0_Status & (1 << CP0St_FR)) {
+                err = kvm_mips_put_one_ureg64(cs, KVM_REG_MIPS_FPR_64(i),
+                                              &env->active_fpu.fpr[i].d);
+            } else {
+                err = kvm_mips_get_one_ureg(cs, KVM_REG_MIPS_FPR_32(i),
+                                      &env->active_fpu.fpr[i].w[FP_ENDIAN_IDX]);
+            }
+            if (err < 0) {
+                DPRINTF("%s: Failed to put FPR%u (%d)\n", __func__, i, err);
+                ret = err;
+            }
+        }
+    }
+
+    return ret;
+}
+
+static int kvm_mips_get_fpu_registers(CPUState *cs)
+{
+    MIPSCPU *cpu = MIPS_CPU(cs);
+    CPUMIPSState *env = &cpu->env;
+    int err, ret = 0;
+    unsigned int i;
+
+    /* Only get FPU state if we're emulating a CPU with an FPU */
+    if (env->CP0_Config1 & (1 << CP0C1_FP)) {
+        /* FPU Control Registers */
+        err = kvm_mips_get_one_ureg(cs, KVM_REG_MIPS_FCR_IR,
+                                    &env->active_fpu.fcr0);
+        if (err < 0) {
+            DPRINTF("%s: Failed to get FCR_IR (%d)\n", __func__, err);
+            ret = err;
+        }
+        err = kvm_mips_get_one_ureg(cs, KVM_REG_MIPS_FCR_CSR,
+                                    &env->active_fpu.fcr31);
+        if (err < 0) {
+            DPRINTF("%s: Failed to get FCR_CSR (%d)\n", __func__, err);
+            ret = err;
+        } else {
+            /* set rounding mode */
+            restore_rounding_mode(env);
+            /* set flush-to-zero mode */
+            restore_flush_mode(env);
+        }
+
+        /* Floating point registers */
+        for (i = 0; i < 32; ++i) {
+            if (env->CP0_Status & (1 << CP0St_FR)) {
+                err = kvm_mips_get_one_ureg64(cs, KVM_REG_MIPS_FPR_64(i),
+                                              &env->active_fpu.fpr[i].d);
+            } else {
+                err = kvm_mips_get_one_ureg(cs, KVM_REG_MIPS_FPR_32(i),
+                                      &env->active_fpu.fpr[i].w[FP_ENDIAN_IDX]);
+            }
+            if (err < 0) {
+                DPRINTF("%s: Failed to get FPR%u (%d)\n", __func__, i, err);
+                ret = err;
+            }
+        }
+    }
+
+    return ret;
+}
+
+
 static int kvm_mips_put_cp0_registers(CPUState *cs, int level)
 {
     MIPSCPU *cpu = MIPS_CPU(cs);
@@ -805,6 +915,11 @@ int kvm_arch_put_registers(CPUState *cs, int level)
         return ret;
     }
 
+    ret = kvm_mips_put_fpu_registers(cs, level);
+    if (ret < 0) {
+        return ret;
+    }
+
     return ret;
 }
 
@@ -832,6 +947,7 @@ int kvm_arch_get_registers(CPUState *cs)
     env->active_tc.PC = regs.pc;
 
     kvm_mips_get_cp0_registers(cs);
+    kvm_mips_get_fpu_registers(cs);
 
     return ret;
 }
-- 
2.4.10