Re: [PATCH v2 14/15] RISC-V: KVM: add support for FWFT SBI extension

["Clément Léger" <cleger@rivosinc.com>]

On 11/02/2025 06:57, Deepak Gupta wrote:
> On Mon, Feb 10, 2025 at 10:35:47PM +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 |  37 ++++
>> 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             | 187 +++++++++++++++++++++
>> 7 files changed, 235 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..5782517f6e08
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
>> @@ -0,0 +1,37 @@
>> +/* 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_vcpu;
>> +
> 
> 
> Can we add some comments here for future fwft providers along below lines?
> 
> Reason being, patch defaults to `conf->supported = true` if `supported` fn
> pointer in `kvm_sbi_fwft_feature` was NULL. Although `kvm_sbi_fwft_set/get`
> does get/set fn pointers (it would happen even if `supported` fn pointer
> was NULL).

Yes sure, I'll add some kernel doc comments.

Thanks,

Clément

> 
>> +struct kvm_sbi_fwft_feature {
>> +    enum sbi_fwft_feature_t id;
>     /* If function not provided, KVM will default assume to be true */
>> +    bool (*supported)(struct kvm_vcpu *vcpu);
>     /* Must always provide function pointers for get/set */
>> +    int (*set)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config
>> *conf, unsigned long value);
>> +    int (*get)(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config
>> *conf, unsigned long *value);
> 
> 
>> +};
>> +
>> +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 f81f06f82650..3b37deaed4e7 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..fe608bf16558
>> --- /dev/null
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> @@ -0,0 +1,187 @@
>> +// 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>
>> +
>> +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;
>> +    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, unsigned long
>> feature,
>> +                struct kvm_sbi_fwft_config **conf)
>> +{
>> +    struct kvm_sbi_fwft_config *tconf;
>> +
>> +    /* Feature are defined as 32 bits identifiers */
>> +    if (feature & ~(BIT_ULL(32) - 1))
>> +        return SBI_ERR_INVALID_PARAM;
>> +
>> +    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, unsigned long
>> 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;
>> +    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
>>
>>


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