Re: [PATCH 1/4] KVM: arm64: Rework detection of SVE, !VHE systems

[Dave Martin]

On Tue, Nov 06, 2018 at 08:52:51AM +0100, Christoffer Dall wrote:
> On Mon, Nov 05, 2018 at 02:36:13PM +, Marc Zyngier wrote:
> > An SVE system is so far the only case where we mandate VHE. As we're
> > starting to grow this requirements, let's slightly rework the way we
> > deal with that situation, allowing for easy extension of this check.
> > 
> > Signed-off-by: Marc Zyngier 
> > ---
> >  arch/arm/include/asm/kvm_host.h   |  2 +-
> >  arch/arm64/include/asm/kvm_host.h |  7 ++-
> >  virt/kvm/arm/arm.c| 12 +++-
> >  3 files changed, 10 insertions(+), 11 deletions(-)
> > 

[...]

> > diff --git a/arch/arm64/include/asm/kvm_host.h 
> > b/arch/arm64/include/asm/kvm_host.h
> > index 52fbc823ff8c..ca1714148400 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -422,17 +422,14 @@ static inline void __cpu_init_hyp_mode(phys_addr_t 
> > pgd_ptr,
> > }
> >  }
> >  
> > -static inline bool kvm_arch_check_sve_has_vhe(void)
> > +static inline bool kvm_arch_sve_requires_vhe(void)
> >  {
> > /*
> >  * The Arm architecture specifies that implementation of SVE
> >  * requires VHE also to be implemented.  The KVM code for arm64
> >  * relies on this when SVE is present:
> >  */
> > -   if (system_supports_sve())
> > -   return has_vhe();
> > -   else
> > -   return true;
> > +   return system_supports_sve();
> >  }
> 
> nit: Can we call this function 'kvm_arch_requires_vhe()' and let it test
> for all the cases (maybe that's coming in future patches though).  I
> just find this naming confusing.

Agreed.  I was never keen on my original name, and the logic was
somewhat backwards anyway.

"kvm_arch_requires_vhe()" is a reasonable name for a function that
returns true iff the kernel needs VHE as a consequence of some other
prior runtime decision.

> >  
> >  static inline void kvm_arch_hardware_unsetup(void) {}
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 23774970c9df..66de2efddfca 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -1640,9 +1640,13 @@ int kvm_arch_init(void *opaque)
> > return -ENODEV;
> > }
> >  
> > -   if (!kvm_arch_check_sve_has_vhe()) {
> > -   kvm_pr_unimpl("SVE system without VHE unsupported.  Broken 
> > cpu?");
> > -   return -ENODEV;
> > +   in_hyp_mode = is_kernel_in_hyp_mode();
> > +
> > +   if (!in_hyp_mode) {
> > +   if (kvm_arch_sve_requires_vhe()) {

Can we just have

if (!in_hyp_mode && kvm_arch_requires_vhe()) {

That's less nesty but still readable (for me, at least).

Otherwise, Ack.


[...]

Cheers
---Dave
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Re: [PATCH 1/4] KVM: arm64: Rework detection of SVE, !VHE systems

[Christoffer Dall]

On Mon, Nov 05, 2018 at 02:36:13PM +, Marc Zyngier wrote:
> An SVE system is so far the only case where we mandate VHE. As we're
> starting to grow this requirements, let's slightly rework the way we
> deal with that situation, allowing for easy extension of this check.
> 
> Signed-off-by: Marc Zyngier 
> ---
>  arch/arm/include/asm/kvm_host.h   |  2 +-
>  arch/arm64/include/asm/kvm_host.h |  7 ++-
>  virt/kvm/arm/arm.c| 12 +++-
>  3 files changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 5ca5d9af0c26..c3469729f40c 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -285,7 +285,7 @@ void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>  
>  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>  
> -static inline bool kvm_arch_check_sve_has_vhe(void) { return true; }
> +static inline bool kvm_arch_sve_requires_vhe(void) { return false; }
>  static inline void kvm_arch_hardware_unsetup(void) {}
>  static inline void kvm_arch_sync_events(struct kvm *kvm) {}
>  static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> diff --git a/arch/arm64/include/asm/kvm_host.h 
> b/arch/arm64/include/asm/kvm_host.h
> index 52fbc823ff8c..ca1714148400 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -422,17 +422,14 @@ static inline void __cpu_init_hyp_mode(phys_addr_t 
> pgd_ptr,
>   }
>  }
>  
> -static inline bool kvm_arch_check_sve_has_vhe(void)
> +static inline bool kvm_arch_sve_requires_vhe(void)
>  {
>   /*
>* The Arm architecture specifies that implementation of SVE
>* requires VHE also to be implemented.  The KVM code for arm64
>* relies on this when SVE is present:
>*/
> - if (system_supports_sve())
> - return has_vhe();
> - else
> - return true;
> + return system_supports_sve();
>  }

nit: Can we call this function 'kvm_arch_requires_vhe()' and let it test
for all the cases (maybe that's coming in future patches though).  I
just find this naming confusing.

>  
>  static inline void kvm_arch_hardware_unsetup(void) {}
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 23774970c9df..66de2efddfca 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1640,9 +1640,13 @@ int kvm_arch_init(void *opaque)
>   return -ENODEV;
>   }
>  
> - if (!kvm_arch_check_sve_has_vhe()) {
> - kvm_pr_unimpl("SVE system without VHE unsupported.  Broken 
> cpu?");
> - return -ENODEV;
> + in_hyp_mode = is_kernel_in_hyp_mode();
> +
> + if (!in_hyp_mode) {
> + if (kvm_arch_sve_requires_vhe()) {
> + kvm_pr_unimpl("SVE system without VHE unsupported.  
> Broken cpu?");
> + return -ENODEV;
> + }
>   }
>  
>   for_each_online_cpu(cpu) {
> @@ -1657,8 +1661,6 @@ int kvm_arch_init(void *opaque)
>   if (err)
>   return err;
>  
> - in_hyp_mode = is_kernel_in_hyp_mode();
> -
>   if (!in_hyp_mode) {
>   err = init_hyp_mode();
>   if (err)
> -- 
> 2.19.1
> 


Thanks,

Christoffer
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[PATCH 1/4] KVM: arm64: Rework detection of SVE, !VHE systems

[Marc Zyngier]

An SVE system is so far the only case where we mandate VHE. As we're
starting to grow this requirements, let's slightly rework the way we
deal with that situation, allowing for easy extension of this check.

Signed-off-by: Marc Zyngier 
---
 arch/arm/include/asm/kvm_host.h   |  2 +-
 arch/arm64/include/asm/kvm_host.h |  7 ++-
 virt/kvm/arm/arm.c| 12 +++-
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 5ca5d9af0c26..c3469729f40c 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -285,7 +285,7 @@ void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
 
 struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
 
-static inline bool kvm_arch_check_sve_has_vhe(void) { return true; }
+static inline bool kvm_arch_sve_requires_vhe(void) { return false; }
 static inline void kvm_arch_hardware_unsetup(void) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
 static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
diff --git a/arch/arm64/include/asm/kvm_host.h 
b/arch/arm64/include/asm/kvm_host.h
index 52fbc823ff8c..ca1714148400 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -422,17 +422,14 @@ static inline void __cpu_init_hyp_mode(phys_addr_t 
pgd_ptr,
}
 }
 
-static inline bool kvm_arch_check_sve_has_vhe(void)
+static inline bool kvm_arch_sve_requires_vhe(void)
 {
/*
 * The Arm architecture specifies that implementation of SVE
 * requires VHE also to be implemented.  The KVM code for arm64
 * relies on this when SVE is present:
 */
-   if (system_supports_sve())
-   return has_vhe();
-   else
-   return true;
+   return system_supports_sve();
 }
 
 static inline void kvm_arch_hardware_unsetup(void) {}
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 23774970c9df..66de2efddfca 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -1640,9 +1640,13 @@ int kvm_arch_init(void *opaque)
return -ENODEV;
}
 
-   if (!kvm_arch_check_sve_has_vhe()) {
-   kvm_pr_unimpl("SVE system without VHE unsupported.  Broken 
cpu?");
-   return -ENODEV;
+   in_hyp_mode = is_kernel_in_hyp_mode();
+
+   if (!in_hyp_mode) {
+   if (kvm_arch_sve_requires_vhe()) {
+   kvm_pr_unimpl("SVE system without VHE unsupported.  
Broken cpu?");
+   return -ENODEV;
+   }
}
 
for_each_online_cpu(cpu) {
@@ -1657,8 +1661,6 @@ int kvm_arch_init(void *opaque)
if (err)
return err;
 
-   in_hyp_mode = is_kernel_in_hyp_mode();
-
if (!in_hyp_mode) {
err = init_hyp_mode();
if (err)
-- 
2.19.1

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