Re: [PATCH v3 16/17] RISC-V: KVM: add support for FWFT SBI extension

Andrew Jones
2025-03-13T15:18:22Z

On Mon, Mar 10, 2025 at 04:12:23PM +0100, Clément Léger wrote:
> Add basic infrastructure to support the FWFT extension in KVM.
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---
> arch/riscv/include/asm/kvm_host.h | 4 +
> arch/riscv/include/asm/kvm_vcpu_sbi.h | 1 +
> arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h | 31 +++
> arch/riscv/include/uapi/asm/kvm.h | 1 +
> arch/riscv/kvm/Makefile | 1 +
> arch/riscv/kvm/vcpu_sbi.c | 4 +
> arch/riscv/kvm/vcpu_sbi_fwft.c | 212 +++++++++++++++++++++
> 7 files changed, 254 insertions(+)
> create mode 100644 arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> create mode 100644 arch/riscv/kvm/vcpu_sbi_fwft.c
>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index bb93d2995ea2..c0db61ba691a 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -19,6 +19,7 @@
> #include <asm/kvm_vcpu_fp.h>
> #include <asm/kvm_vcpu_insn.h>
> #include <asm/kvm_vcpu_sbi.h>
> +#include <asm/kvm_vcpu_sbi_fwft.h>
> #include <asm/kvm_vcpu_timer.h>
> #include <asm/kvm_vcpu_pmu.h>
>
> @@ -281,6 +282,9 @@ struct kvm_vcpu_arch {
> /* Performance monitoring context */
> struct kvm_pmu pmu_context;
>
> + /* Firmware feature SBI extension context */
> + struct kvm_sbi_fwft fwft_context;
> +
> /* 'static' configurations which are set only once */
> struct kvm_vcpu_config cfg;
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index cb68b3a57c8f..ffd03fed0c06 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -98,6 +98,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
> +extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> new file mode 100644
> index 000000000000..ec7568e0dc1a
> --- /dev/null
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2025 Rivos Inc.
> + *
> + * Authors:
> + * Clément Léger <cleger@rivosinc.com>
> + */
> +
> +#ifndef __KVM_VCPU_RISCV_FWFT_H
> +#define __KVM_VCPU_RISCV_FWFT_H
> +
> +#include <asm/sbi.h>
> +
> +struct kvm_sbi_fwft_config;
> +struct kvm_sbi_fwft_feature;
> +struct kvm_vcpu;

Should only need the forward declaration for kvm_sbi_fwft_feature.

> +
> +struct kvm_sbi_fwft_config {
> + const struct kvm_sbi_fwft_feature *feature;
> + bool supported;
> + unsigned long flags;
> +};
> +
> +/* FWFT data structure per vcpu */
> +struct kvm_sbi_fwft {
> + struct kvm_sbi_fwft_config *configs;
> +};
> +
> +#define vcpu_to_fwft(vcpu) (&(vcpu)->arch.fwft_context)
> +
> +#endif /* !__KVM_VCPU_RISCV_FWFT_H */
> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index f06bc5efcd79..fa6eee1caf41 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -202,6 +202,7 @@ enum KVM_RISCV_SBI_EXT_ID {
> KVM_RISCV_SBI_EXT_DBCN,
> KVM_RISCV_SBI_EXT_STA,
> KVM_RISCV_SBI_EXT_SUSP,
> + KVM_RISCV_SBI_EXT_FWFT,
> KVM_RISCV_SBI_EXT_MAX,
> };
>
> diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
> index 4e0bba91d284..06e2d52a9b88 100644
> --- a/arch/riscv/kvm/Makefile
> +++ b/arch/riscv/kvm/Makefile
> @@ -26,6 +26,7 @@ kvm-y += vcpu_onereg.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
> kvm-y += vcpu_sbi.o
> kvm-y += vcpu_sbi_base.o
> +kvm-y += vcpu_sbi_fwft.o
> kvm-y += vcpu_sbi_hsm.o
> kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_sbi_pmu.o
> kvm-y += vcpu_sbi_replace.o
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index 18726096ef44..27f22e98c8f8 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -78,6 +78,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
> .ext_idx = KVM_RISCV_SBI_EXT_STA,
> .ext_ptr = &vcpu_sbi_ext_sta,
> },
> + {
> + .ext_idx = KVM_RISCV_SBI_EXT_FWFT,
> + .ext_ptr = &vcpu_sbi_ext_fwft,
> + },
> {
> .ext_idx = KVM_RISCV_SBI_EXT_EXPERIMENTAL,
> .ext_ptr = &vcpu_sbi_ext_experimental,
> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
> new file mode 100644
> index 000000000000..cce1e41d5490
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> @@ -0,0 +1,212 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2025 Rivos Inc.
> + *
> + * Authors:
> + * Clément Léger <cleger@rivosinc.com>
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/err.h>
> +#include <linux/kvm_host.h>
> +#include <asm/cpufeature.h>
> +#include <asm/sbi.h>
> +#include <asm/kvm_vcpu_sbi.h>
> +#include <asm/kvm_vcpu_sbi_fwft.h>
> +
> +struct kvm_sbi_fwft_feature {
> + /**
> + * @id: Feature ID
> + */
> + enum sbi_fwft_feature_t id;
> +
> + /**
> + * @supported: Check if the feature is supported on the vcpu
> + *
> + * This callback is optional, if not provided the feature is assumed to
> + * be supported
> + */
> + bool (*supported)(struct kvm_vcpu *vcpu);
> +
> + /**
> + * @set: Set the feature value
> + *
> + * This callback is mandatory

Since we're doing all this documentation, then let's also state they
return SBI errors (which are longs, so we should probably return longs).

> + */
> + int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
> +
> + /**
> + * @get: Get the feature current value
> + *
> + * This callback is mandatory
> + */
> + int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long *value);
> +};
> +
> +static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
> + SBI_FWFT_MISALIGNED_EXC_DELEG,
> + SBI_FWFT_LANDING_PAD,
> + SBI_FWFT_SHADOW_STACK,
> + SBI_FWFT_DOUBLE_TRAP,
> + SBI_FWFT_PTE_AD_HW_UPDATING,
> + SBI_FWFT_POINTER_MASKING_PMLEN,
> +};
> +
> +static bool kvm_fwft_is_defined_feature(enum sbi_fwft_feature_t feature)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(kvm_fwft_defined_features); i++) {
> + if (kvm_fwft_defined_features[i] == feature)
> + return true;
> + }
> +
> + return false;
> +}
> +
> +static const struct kvm_sbi_fwft_feature features[] = {
> +};
> +
> +static struct kvm_sbi_fwft_config *
> +kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t feature)
> +{
> + int i = 0;

no need for '= 0'

> + struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
> +
> + for (i = 0; i < ARRAY_SIZE(features); i++) {
> + if (fwft->configs[i].feature->id == feature)
> + return &fwft->configs[i];
> + }
> +
> + return NULL;
> +}
> +
> +static int kvm_fwft_get_feature(struct kvm_vcpu *vcpu, u32 feature,
> + struct kvm_sbi_fwft_config **conf)
> +{
> + struct kvm_sbi_fwft_config *tconf;
> +
> + tconf = kvm_sbi_fwft_get_config(vcpu, feature);
> + if (!tconf) {
> + if (kvm_fwft_is_defined_feature(feature))
> + return SBI_ERR_NOT_SUPPORTED;
> +
> + return SBI_ERR_DENIED;
> + }
> +
> + if (!tconf->supported)
> + return SBI_ERR_NOT_SUPPORTED;
> +
> + *conf = tconf;
> +
> + return SBI_SUCCESS;
> +}
> +
> +static int kvm_sbi_fwft_set(struct kvm_vcpu *vcpu, u32 feature,
> + unsigned long value, unsigned long flags)
> +{
> + int ret;
> + struct kvm_sbi_fwft_config *conf;
> +
> + ret = kvm_fwft_get_feature(vcpu, feature, &conf);
> + if (ret)
> + return ret;
> +
> + if ((flags & ~SBI_FWFT_SET_FLAG_LOCK) != 0)
> + return SBI_ERR_INVALID_PARAM;
> +
> + if (conf->flags & SBI_FWFT_SET_FLAG_LOCK)
> + return SBI_ERR_DENIED_LOCKED;
> +
> + conf->flags = flags;
> +
> + return conf->feature->set(vcpu, conf, value);
> +}
> +
> +static int kvm_sbi_fwft_get(struct kvm_vcpu *vcpu, unsigned long feature,
> + unsigned long *value)
> +{
> + int ret;
> + struct kvm_sbi_fwft_config *conf;
> +
> + ret = kvm_fwft_get_feature(vcpu, feature, &conf);
> + if (ret)
> + return ret;
> +
> + return conf->feature->get(vcpu, conf, value);
> +}
> +
> +static int kvm_sbi_ext_fwft_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
> + struct kvm_vcpu_sbi_return *retdata)
> +{
> + int ret = 0;
> + struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
> + unsigned long funcid = cp->a6;
> +
> + switch (funcid) {
> + case SBI_EXT_FWFT_SET:
> + ret = kvm_sbi_fwft_set(vcpu, cp->a0, cp->a1, cp->a2);
> + break;
> + case SBI_EXT_FWFT_GET:
> + ret = kvm_sbi_fwft_get(vcpu, cp->a0, &retdata->out_val);
> + break;
> + default:
> + ret = SBI_ERR_NOT_SUPPORTED;
> + break;
> + }
> +
> + retdata->err_val = ret;
> +
> + return 0;
> +}
> +
> +static int kvm_sbi_ext_fwft_init(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
> + const struct kvm_sbi_fwft_feature *feature;
> + struct kvm_sbi_fwft_config *conf;
> + int i;
> +
> + fwft->configs = kcalloc(ARRAY_SIZE(features), sizeof(struct kvm_sbi_fwft_config),
> + GFP_KERNEL);
> + if (!fwft->configs)
> + return -ENOMEM;
> +
> + for (i = 0; i < ARRAY_SIZE(features); i++) {
> + feature = &features[i];
> + conf = &fwft->configs[i];
> + if (feature->supported)
> + conf->supported = feature->supported(vcpu);
> + else
> + conf->supported = true;
> +
> + conf->feature = feature;
> + }
> +
> + return 0;
> +}
> +
> +static void kvm_sbi_ext_fwft_deinit(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
> +
> + kfree(fwft->configs);
> +}
> +
> +static void kvm_sbi_ext_fwft_reset(struct kvm_vcpu *vcpu)
> +{
> + int i = 0;

no need for '= 0'

> + struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
> +
> + for (i = 0; i < ARRAY_SIZE(features); i++)
> + fwft->configs[i].flags = 0;
> +}
> +
> +const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft = {
> + .extid_start = SBI_EXT_FWFT,
> + .extid_end = SBI_EXT_FWFT,
> + .handler = kvm_sbi_ext_fwft_handler,
> + .init = kvm_sbi_ext_fwft_init,
> + .deinit = kvm_sbi_ext_fwft_deinit,
> + .reset = kvm_sbi_ext_fwft_reset,
> +};
> --
> 2.47.2
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>