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

[Mario Smarduch]

On 1/10/2016 8:32 AM, Christoffer Dall wrote:
> Hi Mario,
> 
> I spotted one more potential issue...
> 
> 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 at 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"
>>  
>>  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 */
>> +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 */
>> +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;
> 
> Is it correct not to trap VFP registers when the host kernel does not
> have CONFIG_VFPv3?  I think this is a change in functionality compared
> to the current kernels is it not?

With CPU_V7 VFPv3 gets selected, without it fp should be emulated,
with exceptions taken in guest kernel. I don't see a reason why
fp hcptr access should be enabled in that case.

> 
> Thanks,
> -Christoffer
>