Re: [PATCH v6 13/14] RISC-V: KVM: add support for FWFT SBI extension

[Atish Patra <atish.patra@linux.dev>]

On 4/24/25 10:32 AM, Clément Léger wrote:
> Add basic infrastructure to support the FWFT extension in KVM.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.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 |  29 +++
>   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             | 216 +++++++++++++++++++++
>   7 files changed, 256 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 4fa02e082142..c3f880763b9a 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..9ba841355758
> --- /dev/null
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> @@ -0,0 +1,29 @@
> +/* 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_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 5f59fd226cc5..5ba77a3d9f6e 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
> @@ -204,6 +204,7 @@ 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 50be079b5528..0748810c0252 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..b0f66c7bf010
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> @@ -0,0 +1,216 @@
> +// 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
> +	 *
> +	 * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
> +	 *
> +	 * This callback is mandatory
> +	 */
> +	long (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf, unsigned long value);
> +
> +	/**
> +	 * @get: Get the feature current value
> +	 *
> +	 * Return SBI_SUCCESS on success or an SBI error (SBI_ERR_*)
> +	 *
> +	 * This callback is mandatory
> +	 */
> +	long (*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;
> +	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;
> +	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;
> +	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,
> +};

LGTM.
Reviewed-by: Atish Patra <atishp@rivosinc.com>

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