RISC-V: KVM: Support sstc extension

Sstc extension allows the guest to program the vstimecmp CSR directly
instead of making an SBI call to the hypervisor to program the next
event. The timer interrupt is also directly injected to the guest by
the hardware in this case. To maintain backward compatibility, the
hypervisors also update the vstimecmp in an SBI set_time call if
the hardware supports it. Thus, the older kernels in guest also
take advantage of the sstc extension.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Acked-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/all/CAAhSdy2mb6wyqy0NAn9BcTWKMYEc0Z4zU3s3j7oNqBz6eDQ9sg@mail.gmail.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/include/asm/kvm_vcpu_timer.h b/arch/riscv/include/asm/kvm_vcpu_timer.h
index 50138e2eb91b90da96ff0ce12261954ccfc77ca2..0d8fdb8ec63aa2cb1b2f2ec4e00d54100bcaa434 100644 (file)
--- a/arch/riscv/include/asm/kvm_vcpu_timer.h
+++ b/arch/riscv/include/asm/kvm_vcpu_timer.h
@@ -28,6 +28,11 @@ struct kvm_vcpu_timer {
        u64 next_cycles;
        /* Underlying hrtimer instance */
        struct hrtimer hrt;
+
+       /* Flag to check if sstc is enabled or not */
+       bool sstc_enabled;
+       /* A function pointer to switch between stimecmp or hrtimer at runtime */
+       int (*timer_next_event)(struct kvm_vcpu *vcpu, u64 ncycles);
 };
 
 int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu, u64 ncycles);
@@ -40,5 +45,7 @@ int kvm_riscv_vcpu_timer_deinit(struct kvm_vcpu *vcpu);
 int kvm_riscv_vcpu_timer_reset(struct kvm_vcpu *vcpu);
 void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu);
 void kvm_riscv_guest_timer_init(struct kvm *kvm);
+void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu);
+bool kvm_riscv_vcpu_timer_pending(struct kvm_vcpu *vcpu);
 
 #endif

diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 24b2a6e27698743196eb36fec697e6aad54a30af..7351417afd62e32c69eaa6ec9bc57675815ad322 100644 (file)
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -97,6 +97,7 @@ enum KVM_RISCV_ISA_EXT_ID {
        KVM_RISCV_ISA_EXT_I,
        KVM_RISCV_ISA_EXT_M,
        KVM_RISCV_ISA_EXT_SVPBMT,
+       KVM_RISCV_ISA_EXT_SSTC,
        KVM_RISCV_ISA_EXT_MAX,
 };
 

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index 5d271b5976139f92ea38131d4196144625baa1a0..d0f08d5b4282952c82a462cb8f4ba9bc27a5f9eb 100644 (file)
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -52,6 +52,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
        RISCV_ISA_EXT_i,
        RISCV_ISA_EXT_m,
        RISCV_ISA_EXT_SVPBMT,
+       RISCV_ISA_EXT_SSTC,
 };
 
 static unsigned long kvm_riscv_vcpu_base2isa_ext(unsigned long base_ext)
@@ -85,6 +86,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
        case KVM_RISCV_ISA_EXT_C:
        case KVM_RISCV_ISA_EXT_I:
        case KVM_RISCV_ISA_EXT_M:
+       case KVM_RISCV_ISA_EXT_SSTC:
                return false;
        default:
                break;
@@ -203,7 +205,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 
 int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
 {
-       return kvm_riscv_vcpu_has_interrupts(vcpu, 1UL << IRQ_VS_TIMER);
+       return kvm_riscv_vcpu_timer_pending(vcpu);
 }
 
 void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
@@ -785,6 +787,8 @@ static void kvm_riscv_vcpu_update_config(const unsigned long *isa)
        if (__riscv_isa_extension_available(isa, RISCV_ISA_EXT_SVPBMT))
                henvcfg |= ENVCFG_PBMTE;
 
+       if (__riscv_isa_extension_available(isa, RISCV_ISA_EXT_SSTC))
+               henvcfg |= ENVCFG_STCE;
        csr_write(CSR_HENVCFG, henvcfg);
 #ifdef CONFIG_32BIT
        csr_write(CSR_HENVCFGH, henvcfg >> 32);
@@ -828,6 +832,8 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
                                     vcpu->arch.isa);
        kvm_riscv_vcpu_host_fp_restore(&vcpu->arch.host_context);
 
+       kvm_riscv_vcpu_timer_save(vcpu);
+
        csr->vsstatus = csr_read(CSR_VSSTATUS);
        csr->vsie = csr_read(CSR_VSIE);
        csr->vstvec = csr_read(CSR_VSTVEC);

diff --git a/arch/riscv/kvm/vcpu_timer.c b/arch/riscv/kvm/vcpu_timer.c
index 595043857049d082aad53d196ca47685b733a8d1..16f50c46ba39430ee95e0a2a0434ea599671765d 100644 (file)
--- a/arch/riscv/kvm/vcpu_timer.c
+++ b/arch/riscv/kvm/vcpu_timer.c
@@ -69,7 +69,18 @@ static int kvm_riscv_vcpu_timer_cancel(struct kvm_vcpu_timer *t)
        return 0;
 }
 
-int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu, u64 ncycles)
+static int kvm_riscv_vcpu_update_vstimecmp(struct kvm_vcpu *vcpu, u64 ncycles)
+{
+#if defined(CONFIG_32BIT)
+               csr_write(CSR_VSTIMECMP, ncycles & 0xFFFFFFFF);
+               csr_write(CSR_VSTIMECMPH, ncycles >> 32);
+#else
+               csr_write(CSR_VSTIMECMP, ncycles);
+#endif
+               return 0;
+}
+
+static int kvm_riscv_vcpu_update_hrtimer(struct kvm_vcpu *vcpu, u64 ncycles)
 {
        struct kvm_vcpu_timer *t = &vcpu->arch.timer;
        struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
@@ -88,6 +99,65 @@ int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu, u64 ncycles)
        return 0;
 }
 
+int kvm_riscv_vcpu_timer_next_event(struct kvm_vcpu *vcpu, u64 ncycles)
+{
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+
+       return t->timer_next_event(vcpu, ncycles);
+}
+
+static enum hrtimer_restart kvm_riscv_vcpu_vstimer_expired(struct hrtimer *h)
+{
+       u64 delta_ns;
+       struct kvm_vcpu_timer *t = container_of(h, struct kvm_vcpu_timer, hrt);
+       struct kvm_vcpu *vcpu = container_of(t, struct kvm_vcpu, arch.timer);
+       struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
+
+       if (kvm_riscv_current_cycles(gt) < t->next_cycles) {
+               delta_ns = kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t);
+               hrtimer_forward_now(&t->hrt, ktime_set(0, delta_ns));
+               return HRTIMER_RESTART;
+       }
+
+       t->next_set = false;
+       kvm_vcpu_kick(vcpu);
+
+       return HRTIMER_NORESTART;
+}
+
+bool kvm_riscv_vcpu_timer_pending(struct kvm_vcpu *vcpu)
+{
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+       struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
+
+       if (!kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t) ||
+           kvm_riscv_vcpu_has_interrupts(vcpu, 1UL << IRQ_VS_TIMER))
+               return true;
+       else
+               return false;
+}
+
+static void kvm_riscv_vcpu_timer_blocking(struct kvm_vcpu *vcpu)
+{
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+       struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
+       u64 delta_ns;
+
+       if (!t->init_done)
+               return;
+
+       delta_ns = kvm_riscv_delta_cycles2ns(t->next_cycles, gt, t);
+       if (delta_ns) {
+               hrtimer_start(&t->hrt, ktime_set(0, delta_ns), HRTIMER_MODE_REL);
+               t->next_set = true;
+       }
+}
+
+static void kvm_riscv_vcpu_timer_unblocking(struct kvm_vcpu *vcpu)
+{
+       kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
+}
+
 int kvm_riscv_vcpu_get_reg_timer(struct kvm_vcpu *vcpu,
                                 const struct kvm_one_reg *reg)
 {
@@ -180,10 +250,20 @@ int kvm_riscv_vcpu_timer_init(struct kvm_vcpu *vcpu)
                return -EINVAL;
 
        hrtimer_init(&t->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
-       t->hrt.function = kvm_riscv_vcpu_hrtimer_expired;
        t->init_done = true;
        t->next_set = false;
 
+       /* Enable sstc for every vcpu if available in hardware */
+       if (riscv_isa_extension_available(NULL, SSTC)) {
+               t->sstc_enabled = true;
+               t->hrt.function = kvm_riscv_vcpu_vstimer_expired;
+               t->timer_next_event = kvm_riscv_vcpu_update_vstimecmp;
+       } else {
+               t->sstc_enabled = false;
+               t->hrt.function = kvm_riscv_vcpu_hrtimer_expired;
+               t->timer_next_event = kvm_riscv_vcpu_update_hrtimer;
+       }
+
        return 0;
 }
 
@@ -199,21 +279,73 @@ int kvm_riscv_vcpu_timer_deinit(struct kvm_vcpu *vcpu)
 
 int kvm_riscv_vcpu_timer_reset(struct kvm_vcpu *vcpu)
 {
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+
+       t->next_cycles = -1ULL;
        return kvm_riscv_vcpu_timer_cancel(&vcpu->arch.timer);
 }
 
-void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu)
+static void kvm_riscv_vcpu_update_timedelta(struct kvm_vcpu *vcpu)
 {
        struct kvm_guest_timer *gt = &vcpu->kvm->arch.timer;
 
-#ifdef CONFIG_64BIT
-       csr_write(CSR_HTIMEDELTA, gt->time_delta);
-#else
+#if defined(CONFIG_32BIT)
        csr_write(CSR_HTIMEDELTA, (u32)(gt->time_delta));
        csr_write(CSR_HTIMEDELTAH, (u32)(gt->time_delta >> 32));
+#else
+       csr_write(CSR_HTIMEDELTA, gt->time_delta);
 #endif
 }
 
+void kvm_riscv_vcpu_timer_restore(struct kvm_vcpu *vcpu)
+{
+       struct kvm_vcpu_csr *csr;
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+
+       kvm_riscv_vcpu_update_timedelta(vcpu);
+
+       if (!t->sstc_enabled)
+               return;
+
+       csr = &vcpu->arch.guest_csr;
+#if defined(CONFIG_32BIT)
+       csr_write(CSR_VSTIMECMP, (u32)t->next_cycles);
+       csr_write(CSR_VSTIMECMPH, (u32)(t->next_cycles >> 32));
+#else
+       csr_write(CSR_VSTIMECMP, t->next_cycles);
+#endif
+
+       /* timer should be enabled for the remaining operations */
+       if (unlikely(!t->init_done))
+               return;
+
+       kvm_riscv_vcpu_timer_unblocking(vcpu);
+}
+
+void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu)
+{
+       struct kvm_vcpu_csr *csr;
+       struct kvm_vcpu_timer *t = &vcpu->arch.timer;
+
+       if (!t->sstc_enabled)
+               return;
+
+       csr = &vcpu->arch.guest_csr;
+       t = &vcpu->arch.timer;
+#if defined(CONFIG_32BIT)
+       t->next_cycles = csr_read(CSR_VSTIMECMP);
+       t->next_cycles |= (u64)csr_read(CSR_VSTIMECMPH) << 32;
+#else
+       t->next_cycles = csr_read(CSR_VSTIMECMP);
+#endif
+       /* timer should be enabled for the remaining operations */
+       if (unlikely(!t->init_done))
+               return;
+
+       if (kvm_vcpu_is_blocking(vcpu))
+               kvm_riscv_vcpu_timer_blocking(vcpu);
+}
+
 void kvm_riscv_guest_timer_init(struct kvm *kvm)
 {
        struct kvm_guest_timer *gt = &kvm->arch.timer;