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

[Deepak Gupta <debug@rivosinc.com>]

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;
>+
>+struct kvm_sbi_fwft_feature {
>+	enum sbi_fwft_feature_t id;
>+	bool (*supported)(struct kvm_vcpu *vcpu);
>+	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);
nit:

I understand that in next patch you grow the static array`features`. But in this patch
`ARRAY_SIZE(features)` evaluates to 0, thus kcalloc will be returning a pointer
to some slab block (IIRC, kcalloc will not return NULL if size eventually evals to 0)

This probably won't result in some bad stuff. But still there is a pointer in
fwft->configs which is pointing to some random stuff if `features` turns out to be
empty.

Let me know if I got that right or missing something.

>+	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
>
>