Re: [PATCH v6 1/6] arm/arm64: KVM: Introduce armv7 fp/simd vcpu fields and helpers

[Christoffer Dall <christoffer.dall@linaro.org>]

On Sat, Dec 26, 2015 at 01:54:55PM -0800, Mario Smarduch wrote:
> Add helper functions to enable access to fp/smid on guest entry and save host
> fpexc on vcpu put, check if fp/simd registers are dirty and add new vcpu
> fields.
> 
> Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
> ---
>  arch/arm/include/asm/kvm_emulate.h   | 42 ++++++++++++++++++++++++++++++++++++
>  arch/arm/include/asm/kvm_host.h      |  6 ++++++
>  arch/arm64/include/asm/kvm_emulate.h |  8 +++++++
>  3 files changed, 56 insertions(+)
> 
> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
> index 3095df0..d4d9da1 100644
> --- a/arch/arm/include/asm/kvm_emulate.h
> +++ b/arch/arm/include/asm/kvm_emulate.h
> @@ -24,6 +24,8 @@
>  #include <asm/kvm_mmio.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/cputype.h>
> +#include <asm/vfp.h>
> +#include "../vfp/vfpinstr.h"

this looks dodgy...

can you move vfpinstr.h instead?

>  
>  unsigned long *vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num);
>  unsigned long *vcpu_spsr(struct kvm_vcpu *vcpu);
> @@ -255,4 +257,44 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>  	}
>  }
>  
> +#ifdef CONFIG_VFPv3
> +/* Called from vcpu_load - save fpexc and enable guest access to fp/simd unit */

the comment is misleading, you're not enabling guest access to the
fp/simd unit, you're just setting the enabled bit to ensure guest
accesses trap.

> +static inline void vcpu_trap_vfp_enable(struct kvm_vcpu *vcpu)
> +{
> +	u32 fpexc;
> +
> +	/* Save host fpexc, and enable guest access to fp unit */
> +	fpexc = fmrx(FPEXC);
> +	vcpu->arch.host_fpexc = fpexc;
> +	fpexc |= FPEXC_EN;
> +	fmxr(FPEXC, fpexc);
> +
> +	/* Configure HCPTR to trap on tracing and fp/simd access */
> +	vcpu->arch.hcptr = HCPTR_TTA | HCPTR_TCP(10)  | HCPTR_TCP(11);
> +}
> +
> +/* Called from vcpu_put - restore host fpexc */

I would probably get rid of the "Called from" stuff and just describe
what these functions do locally.  Comments like this are likely to be
out of date soon'ish.

> +static inline void vcpu_restore_host_fpexc(struct kvm_vcpu *vcpu)
> +{
> +	fmxr(FPEXC, vcpu->arch.host_fpexc);
> +}
> +
> +/* If trap bits are reset then fp/simd registers are dirty */
> +static inline bool vcpu_vfp_isdirty(struct kvm_vcpu *vcpu)
> +{
> +	return !(vcpu->arch.hcptr & (HCPTR_TCP(10) | HCPTR_TCP(11)));
> +}
> +#else
> +static inline void vcpu_trap_vfp_enable(struct kvm_vcpu *vcpu)
> +{
> +	vcpu->arch.hcptr = HCPTR_TTA;
> +}
> +
> +static inline void vcpu_restore_host_fpexc(struct kvm_vcpu *vcpu) {}
> +static inline bool vcpu_vfp_isdirty(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +#endif

this kind of feels like it belongs in its own C-file instead of a header
file, perhaps arch/arm/kvm/vfp.C.

Marc, what do you think?

> +
>  #endif /* __ARM_KVM_EMULATE_H__ */
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index f9f2779..d3ef58a 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -105,6 +105,12 @@ struct kvm_vcpu_arch {
>  	/* HYP trapping configuration */
>  	u32 hcr;
>  
> +	/* HYP Co-processor fp/simd and trace trapping configuration */
> +	u32 hcptr;
> +
> +	/* Save host FPEXC register to later restore on vcpu put */
> +	u32 host_fpexc;
> +
>  	/* Interrupt related fields */
>  	u32 irq_lines;		/* IRQ and FIQ levels */
>  
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 3066328..ffe8ccf 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -299,4 +299,12 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>  	return data;		/* Leave LE untouched */
>  }
>  
> +static inline void vcpu_trap_vfp_enable(struct kvm_vcpu *vcpu) {}
> +static inline void vcpu_restore_host_fpexc(struct kvm_vcpu *vcpu) {}
> +
> +static inline bool vcpu_vfp_isdirty(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  #endif /* __ARM64_KVM_EMULATE_H__ */
> -- 
> 1.9.1
> 

Thanks,
-Christoffer