On 1/14/2016 5:27 AM, Christoffer Dall wrote:
> On Wed, Jan 13, 2016 at 07:03:04PM -0800, Mario Smarduch wrote:
>>
>>
>> On 1/12/2016 4:57 PM, Mario Smarduch wrote:
>>>
>>>
>>> On 1/12/2016 6:12 AM, Christoffer Dall wrote:
>>>> On Mon, Jan 11, 2016 at 03:39:21PM -0800, Mario Smarduch wrote:
>>>>>
>>>>>
>>>>> 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@xxxxxxxxxxx>
>>>>>>> ---
>>>>>>> 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.
>>>>>
>>>>
>>>> If you have to guests with CONFIG_VFPV3 but your host doesn't have
>>>> CONFIG_VFPV3, you will never context-switch the VFP registers between
>>>> the two VMs, and mayhem will ensue.
>>>>
>>>> Unless I'm missing something very obvious?
>>
>> Did more testing on this enabling OABI_COMPAT and selecting
>> NWFPE/FastFPE breaks the boot. So far can't find a way to boot host
>> without VFP/VFPv3 enabled on ARMv7. CPU_V7 defaults to VFPv3
>> selection. I'm wondering if !VFPv3 path should be removed from
>> the patches?
>>
> I think this is related to your particular choice of userspace.
It appears like there are two soft float implementations.
FastFPE - but that's missing arch/arm/fastfpe directory, the option
can still be selected but nothing is built.
And the Netwidner FPE arch/arm/nwfpe, that doesn't appear to be
hooked into the kernel. The hook nwfpe_enter is not referenced
anywhere.
I could make this change but have no way to bring the host up to
test it.
- Mario
> I think
> it's fair to assume VFP is enabled for a KVM host, but I don't have
> enough familiarity with this to be sure.
>
> Marc, any thoughts?
>
> -Christoffer
>
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