Re: [PATCH v2 1/1] RISC-V: KVM: Add ONE_REG interface to enable/disable SBI extensions

From: Andrew Jones
Date: Thu Mar 30 2023 - 03:04:56 EST

On Thu, Mar 30, 2023 at 11:01:35AM +0530, Anup Patel wrote:
> We add ONE_REG interface to enable/disable SBI extensions (just
> like the ONE_REG interface for ISA extensions). This allows KVM
> user-space to decide the set of SBI extension enabled for a Guest
> and by default all SBI extensions are enabled.
>
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
> arch/riscv/include/asm/kvm_vcpu_sbi.h | 8 +-
> arch/riscv/include/uapi/asm/kvm.h | 20 ++++
> arch/riscv/kvm/vcpu.c | 2 +
> arch/riscv/kvm/vcpu_sbi.c | 150 +++++++++++++++++++++++---
> arch/riscv/kvm/vcpu_sbi_base.c | 2 +-
> 5 files changed, 163 insertions(+), 19 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index 8425556af7d1..4278125a38a5 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -16,6 +16,7 @@
>
> struct kvm_vcpu_sbi_context {
> int return_handled;
> + bool extension_disabled[KVM_RISCV_SBI_EXT_MAX];
> };
>
> struct kvm_vcpu_sbi_return {
> @@ -45,7 +46,12 @@ void kvm_riscv_vcpu_sbi_system_reset(struct kvm_vcpu *vcpu,
> struct kvm_run *run,
> u32 type, u64 flags);
> int kvm_riscv_vcpu_sbi_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
> -const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(unsigned long extid);
> +int kvm_riscv_vcpu_set_reg_sbi_ext(struct kvm_vcpu *vcpu,
> + const struct kvm_one_reg *reg);
> +int kvm_riscv_vcpu_get_reg_sbi_ext(struct kvm_vcpu *vcpu,
> + const struct kvm_one_reg *reg);
> +const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
> + struct kvm_vcpu *vcpu, unsigned long extid);
> int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run);
>
> #ifdef CONFIG_RISCV_SBI_V01
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 92af6f3f057c..33c3457b94e7 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -108,6 +108,23 @@ enum KVM_RISCV_ISA_EXT_ID {
> KVM_RISCV_ISA_EXT_MAX,
> };
>
> +/*
> + * SBI extension IDs specific to KVM. This is not the same as the SBI
> + * extension IDs defined by the RISC-V SBI specification.
> + */
> +enum KVM_RISCV_SBI_EXT_ID {
> + KVM_RISCV_SBI_EXT_V01 = 0,
> + KVM_RISCV_SBI_EXT_TIME,
> + KVM_RISCV_SBI_EXT_IPI,
> + KVM_RISCV_SBI_EXT_RFENCE,
> + KVM_RISCV_SBI_EXT_SRST,
> + KVM_RISCV_SBI_EXT_HSM,
> + KVM_RISCV_SBI_EXT_PMU,
> + KVM_RISCV_SBI_EXT_EXPERIMENTAL,
> + KVM_RISCV_SBI_EXT_VENDOR,
> + KVM_RISCV_SBI_EXT_MAX,
> +};
> +
> /* Possible states for kvm_riscv_timer */
> #define KVM_RISCV_TIMER_STATE_OFF 0
> #define KVM_RISCV_TIMER_STATE_ON 1
> @@ -152,6 +169,9 @@ enum KVM_RISCV_ISA_EXT_ID {
> /* ISA Extension registers are mapped as type 7 */
> #define KVM_REG_RISCV_ISA_EXT (0x07 << KVM_REG_RISCV_TYPE_SHIFT)
>
> +/* SBI extension registers are mapped as type 8 */
> +#define KVM_REG_RISCV_SBI_EXT (0x08 << KVM_REG_RISCV_TYPE_SHIFT)
> +
> #endif
>
> #endif /* __LINUX_KVM_RISCV_H */
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index 7d010b0be54e..311fd347c5a8 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -601,6 +601,8 @@ static int kvm_riscv_vcpu_set_reg(struct kvm_vcpu *vcpu,
> KVM_REG_RISCV_FP_D);
> case KVM_REG_RISCV_ISA_EXT:
> return kvm_riscv_vcpu_set_reg_isa_ext(vcpu, reg);
> + case KVM_REG_RISCV_SBI_EXT:
> + return kvm_riscv_vcpu_set_reg_sbi_ext(vcpu, reg);
> default:
> break;
> }
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index 15fde15f9fb8..bedd7d78a5f0 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -30,17 +30,52 @@ static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
> };
> #endif
>
> -static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
> - &vcpu_sbi_ext_v01,
> - &vcpu_sbi_ext_base,
> - &vcpu_sbi_ext_time,
> - &vcpu_sbi_ext_ipi,
> - &vcpu_sbi_ext_rfence,
> - &vcpu_sbi_ext_srst,
> - &vcpu_sbi_ext_hsm,
> - &vcpu_sbi_ext_pmu,
> - &vcpu_sbi_ext_experimental,
> - &vcpu_sbi_ext_vendor,
> +struct kvm_riscv_sbi_extension_entry {
> + enum KVM_RISCV_SBI_EXT_ID dis_idx;
> + const struct kvm_vcpu_sbi_extension *ext_ptr;
> +};
> +
> +static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_V01,
> + .ext_ptr = &vcpu_sbi_ext_v01,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_MAX, /* Can't be disabled */
> + .ext_ptr = &vcpu_sbi_ext_base,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_TIME,
> + .ext_ptr = &vcpu_sbi_ext_time,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_IPI,
> + .ext_ptr = &vcpu_sbi_ext_ipi,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_RFENCE,
> + .ext_ptr = &vcpu_sbi_ext_rfence,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_SRST,
> + .ext_ptr = &vcpu_sbi_ext_srst,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_HSM,
> + .ext_ptr = &vcpu_sbi_ext_hsm,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_PMU,
> + .ext_ptr = &vcpu_sbi_ext_pmu,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
> + .ext_ptr = &vcpu_sbi_ext_experimental,
> + },
> + {
> + .dis_idx = KVM_RISCV_SBI_EXT_VENDOR,
> + .ext_ptr = &vcpu_sbi_ext_vendor,
> + },
> };
>
> void kvm_riscv_vcpu_sbi_forward(struct kvm_vcpu *vcpu, struct kvm_run *run)
> @@ -99,14 +134,95 @@ int kvm_riscv_vcpu_sbi_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
> return 0;
> }
>
> -const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(unsigned long extid)
> +int kvm_riscv_vcpu_set_reg_sbi_ext(struct kvm_vcpu *vcpu,
> + const struct kvm_one_reg *reg)
> +{
> + unsigned long __user *uaddr =
> + (unsigned long __user *)(unsigned long)reg->addr;
> + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> + KVM_REG_SIZE_MASK |
> + KVM_REG_RISCV_SBI_EXT);
> + unsigned long i, reg_val;
> + const struct kvm_riscv_sbi_extension_entry *sext = NULL;
> + struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
> +
> + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> + return -EINVAL;
> +
> + if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
> + return -EFAULT;
> +
> + if (reg_num >= KVM_RISCV_SBI_EXT_MAX ||
> + (reg_val != 1 && reg_val != 0))
> + return -EINVAL;
> +
> + if (vcpu->arch.ran_atleast_once)
> + return -EBUSY;
> +
> + for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
> + if (sbi_ext[i].dis_idx == reg_num) {
> + sext = &sbi_ext[i];
> + break;
> + }
> + }
> + if (!sext)
> + return -ENOENT;
> +
> + scontext->extension_disabled[sext->dis_idx] = !reg_val;
> +
> + return 0;
> +}
> +
> +int kvm_riscv_vcpu_get_reg_sbi_ext(struct kvm_vcpu *vcpu,
> + const struct kvm_one_reg *reg)
> +{
> + unsigned long __user *uaddr =
> + (unsigned long __user *)(unsigned long)reg->addr;
> + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> + KVM_REG_SIZE_MASK |
> + KVM_REG_RISCV_SBI_EXT);
> + unsigned long i, reg_val;
> + const struct kvm_riscv_sbi_extension_entry *sext = NULL;
> + struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
> +
> + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> + return -EINVAL;
> +
> + if (reg_num >= KVM_RISCV_SBI_EXT_MAX)
> + return -EINVAL;
> +
> + for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
> + if (sbi_ext[i].dis_idx == reg_num) {
> + sext = &sbi_ext[i];
> + break;
> + }
> + }
> + if (!sext)
> + return -ENOENT;
> +
> + reg_val = !scontext->extension_disabled[sext->dis_idx];
> + if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
> +const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
> + struct kvm_vcpu *vcpu, unsigned long extid)
> {
> - int i = 0;
> + int i;
> + const struct kvm_riscv_sbi_extension_entry *sext;
> + struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
>
> for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
> - if (sbi_ext[i]->extid_start <= extid &&
> - sbi_ext[i]->extid_end >= extid)
> - return sbi_ext[i];
> + sext = &sbi_ext[i];
> + if (sext->ext_ptr->extid_start <= extid &&
> + sext->ext_ptr->extid_end >= extid) {
> + if (sext->dis_idx < KVM_RISCV_SBI_EXT_MAX &&
> + scontext->extension_disabled[sext->dis_idx])
> + return NULL;
> + return sbi_ext[i].ext_ptr;
> + }
> }
>
> return NULL;
> @@ -126,7 +242,7 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run)
> };
> bool ext_is_v01 = false;
>
> - sbi_ext = kvm_vcpu_sbi_find_ext(cp->a7);
> + sbi_ext = kvm_vcpu_sbi_find_ext(vcpu, cp->a7);
> if (sbi_ext && sbi_ext->handler) {
> #ifdef CONFIG_RISCV_SBI_V01
> if (cp->a7 >= SBI_EXT_0_1_SET_TIMER &&
> diff --git a/arch/riscv/kvm/vcpu_sbi_base.c b/arch/riscv/kvm/vcpu_sbi_base.c
> index 9945aff34c14..5bc570b984f4 100644
> --- a/arch/riscv/kvm/vcpu_sbi_base.c
> +++ b/arch/riscv/kvm/vcpu_sbi_base.c
> @@ -44,7 +44,7 @@ static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
> kvm_riscv_vcpu_sbi_forward(vcpu, run);
> retdata->uexit = true;
> } else {
> - sbi_ext = kvm_vcpu_sbi_find_ext(cp->a0);
> + sbi_ext = kvm_vcpu_sbi_find_ext(vcpu, cp->a0);
> *out_val = sbi_ext && sbi_ext->probe ?
> sbi_ext->probe(vcpu) : !!sbi_ext;
> }
> --
> 2.34.1
>

This looks good, but I wonder if we shouldn't instead get/set a bitmap of
all SBI extension enables at once for scalability.

Thanks,
drew