diff mbox series

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

Message ID 20231012051509.738750-4-apatel@ventanamicro.com
State New
Headers
Series RISC-V SBI debug console extension support |

Commit Message

Anup Patel Oct. 12, 2023, 5:15 a.m. UTC 
  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(-)

Comments

Andrew Jones Oct. 19, 2023, 7:57 a.m. UTC | #1 
On Thu, Oct 12, 2023 at 10:45:04AM +0530, Anup Patel wrote:
> 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);

With this, we no longer defer probing to the first access (whether that's
by the guest or KVM userspace). With our current small set of SBI
extensions where only a single one has a probe function, then this
simpler approach is good enough. We can always go back to the lazy
approach later if needed.

> +
>  	/* 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;

We're missing the change to riscv_vcpu_get_sbi_ext_single() which should
also drop the comment block explaining the limits to status knowledge
without initial probing (which we now do) and then just check for
available, i.e.

diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index bb76c3cf633f..92c42d9aba1c 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -186,15 +186,8 @@ static int riscv_vcpu_get_sbi_ext_single(struct kvm_vcpu *vcpu,
 	if (!sext)
 		return -ENOENT;
 
-	/*
-	 * If the extension status is still uninitialized, then we should probe
-	 * to determine if it's available, but it may be too early to do that
-	 * here. The best we can do is report that the extension has not been
-	 * disabled, i.e. we return 1 when the extension is available and also
-	 * when it only may be available.
-	 */
-	*reg_val = scontext->ext_status[sext->ext_idx] !=
-				KVM_RISCV_SBI_EXT_UNAVAILABLE;
+	*reg_val = scontext->ext_status[sext->ext_idx] ==
+				KVM_RISCV_SBI_EXT_AVAILABLE;
 
 	return 0;
 }

>  
>  	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
>

Thanks,
drew
Anup Patel Oct. 20, 2023, 5:26 a.m. UTC | #2 
On Thu, Oct 19, 2023 at 1:27 PM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> On Thu, Oct 12, 2023 at 10:45:04AM +0530, Anup Patel wrote:
> > 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);
>
> With this, we no longer defer probing to the first access (whether that's
> by the guest or KVM userspace). With our current small set of SBI
> extensions where only a single one has a probe function, then this
> simpler approach is good enough. We can always go back to the lazy
> approach later if needed.

I agree. We can fallback to lazy probing in the future if required.

>
> > +
> >       /* 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;
>
> We're missing the change to riscv_vcpu_get_sbi_ext_single() which should
> also drop the comment block explaining the limits to status knowledge
> without initial probing (which we now do) and then just check for
> available, i.e.
>
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index bb76c3cf633f..92c42d9aba1c 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -186,15 +186,8 @@ static int riscv_vcpu_get_sbi_ext_single(struct kvm_vcpu *vcpu,
>         if (!sext)
>                 return -ENOENT;
>
> -       /*
> -        * If the extension status is still uninitialized, then we should probe
> -        * to determine if it's available, but it may be too early to do that
> -        * here. The best we can do is report that the extension has not been
> -        * disabled, i.e. we return 1 when the extension is available and also
> -        * when it only may be available.
> -        */
> -       *reg_val = scontext->ext_status[sext->ext_idx] !=
> -                               KVM_RISCV_SBI_EXT_UNAVAILABLE;
> +       *reg_val = scontext->ext_status[sext->ext_idx] ==
> +                               KVM_RISCV_SBI_EXT_AVAILABLE;
>
>         return 0;
>  }

Thanks, I will include this change in the next revision.

>
> >
> >       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
> >
>
> Thanks,
> drew

Regards,
Anup
diff mbox series

Patch

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;
+	}
+}