[PATCH v2 3/8] RISC-V: KVM: Allow some SBI extensions to be disabled by default

Anup Patel
2023-10-12T05:16:01Z

Currently, all SBI extensions are enabled by default which is
problematic for SBI extensions (such as DBCN) which are forwarded
to the KVM user-space because we might have an older KVM user-space
which is not aware/ready to handle newer SBI extensions. Ideally,
the SBI extensions forwarded to the KVM user-space must be
disabled by default.

To address above, we allow certain SBI extensions to be disabled
by default so that KVM user-space must explicitly enable such
SBI extensions to receive forwarded calls from Guest VCPU.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
---
arch/riscv/include/asm/kvm_vcpu_sbi.h | 4 +++
arch/riscv/kvm/vcpu.c | 6 ++++
arch/riscv/kvm/vcpu_sbi.c | 45 ++++++++++++++++-----------
3 files changed, 36 insertions(+), 19 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index 8d6d4dce8a5e..c02bda5559d7 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -35,6 +35,9 @@ struct kvm_vcpu_sbi_return {
struct kvm_vcpu_sbi_extension {
unsigned long extid_start;
unsigned long extid_end;
+
+ bool default_unavail;
+
/**
* SBI extension handler. It can be defined for a given extension or group of
* extension. But it should always return linux error codes rather than SBI
@@ -59,6 +62,7 @@ int kvm_riscv_vcpu_get_reg_sbi_ext(struct kvm_vcpu *vcpu,
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);
+void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu);

#ifdef CONFIG_RISCV_SBI_V01
extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01;
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index c061a1c5fe98..e087c809073c 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -141,6 +141,12 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
if (rc)
return rc;

+ /*
+ * Setup SBI extensions
+ * NOTE: This must be the last thing to be initialized.
+ */
+ kvm_riscv_vcpu_sbi_init(vcpu);
+
/* Reset VCPU */
kvm_riscv_reset_vcpu(vcpu);

diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index 9cd97091c723..1b1cee86efda 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -155,14 +155,8 @@ static int riscv_vcpu_set_sbi_ext_single(struct kvm_vcpu *vcpu,
if (!sext)
return -ENOENT;

- /*
- * We can't set the extension status to available here, since it may
- * have a probe() function which needs to confirm availability first,
- * but it may be too early to call that here. We can set the status to
- * unavailable, though.
- */
- if (!reg_val)
- scontext->ext_status[sext->ext_idx] =
+ scontext->ext_status[sext->ext_idx] = (reg_val) ?
+ KVM_RISCV_SBI_EXT_AVAILABLE :
KVM_RISCV_SBI_EXT_UNAVAILABLE;

return 0;
@@ -337,18 +331,8 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
scontext->ext_status[entry->ext_idx] ==
KVM_RISCV_SBI_EXT_AVAILABLE)
return ext;
- if (scontext->ext_status[entry->ext_idx] ==
- KVM_RISCV_SBI_EXT_UNAVAILABLE)
- return NULL;
- if (ext->probe && !ext->probe(vcpu)) {
- scontext->ext_status[entry->ext_idx] =
- KVM_RISCV_SBI_EXT_UNAVAILABLE;
- return NULL;
- }

- scontext->ext_status[entry->ext_idx] =
- KVM_RISCV_SBI_EXT_AVAILABLE;
- return ext;
+ return NULL;
}
}

@@ -419,3 +403,26 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run)

return ret;
}
+
+void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
+ const struct kvm_riscv_sbi_extension_entry *entry;
+ const struct kvm_vcpu_sbi_extension *ext;
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
+ entry = &sbi_ext[i];
+ ext = entry->ext_ptr;
+
+ if (ext->probe && !ext->probe(vcpu)) {
+ scontext->ext_status[entry->ext_idx] =
+ KVM_RISCV_SBI_EXT_UNAVAILABLE;
+ continue;
+ }
+
+ scontext->ext_status[entry->ext_idx] = ext->default_unavail ?
+ KVM_RISCV_SBI_EXT_UNAVAILABLE :
+ KVM_RISCV_SBI_EXT_AVAILABLE;
+ }
+}
--
2.34.1