[PATCH 2/2] kvm/arm64: Detach ESR operator from vCPU struct
Gavin Shan
gshan at redhat.com
Mon Jun 29 20:16:07 EDT 2020
Hi Mark,
On 6/29/20 9:00 PM, Mark Rutland wrote:
> On Mon, Jun 29, 2020 at 07:18:41PM +1000, Gavin Shan wrote:
>> There are a set of inline functions defined in kvm_emulate.h. Those
>> functions reads ESR from vCPU fault information struct and then operate
>> on it. So it's tied with vCPU fault information and vCPU struct. It
>> limits their usage scope.
>>
>> This detaches these functions from the vCPU struct by introducing an
>> other set of inline functions in esr.h to manupulate the specified
>> ESR value. With it, the inline functions defined in kvm_emulate.h
>> can call these inline functions (in esr.h) instead. This shouldn't
>> cause any functional changes.
>>
>> Signed-off-by: Gavin Shan <gshan at redhat.com>
>
> TBH, I'm not sure that this patch makes much sense on its own.
>
> We already use vcpu_get_esr(), which is the bit that'd have to change if
> we didn't pass the vcpu around, and the new helpers are just consuming
> the value in a sifferent way rather than a necessarily simpler way.
>
> Further comments on that front below.
>
>> ---
>> arch/arm64/include/asm/esr.h | 32 +++++++++++++++++++++
>> arch/arm64/include/asm/kvm_emulate.h | 43 ++++++++++++----------------
>> 2 files changed, 51 insertions(+), 24 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
>> index 035003acfa87..950204c5fbe1 100644
>> --- a/arch/arm64/include/asm/esr.h
>> +++ b/arch/arm64/include/asm/esr.h
>> @@ -326,6 +326,38 @@ static inline bool esr_is_data_abort(u32 esr)
>> return ec == ESR_ELx_EC_DABT_LOW || ec == ESR_ELx_EC_DABT_CUR;
>> }
>>
>> +#define ESR_DECLARE_CHECK_FUNC(name, field) \
>> +static inline bool esr_is_##name(u32 esr) \
>> +{ \
>> + return !!(esr & (field)); \
>> +}
>> +#define ESR_DECLARE_GET_FUNC(name, mask, shift) \
>> +static inline u32 esr_get_##name(u32 esr) \
>> +{ \
>> + return ((esr & (mask)) >> (shift)); \
>> +}
>> +
>> +ESR_DECLARE_CHECK_FUNC(il_32bit, ESR_ELx_IL);
>> +ESR_DECLARE_CHECK_FUNC(condition, ESR_ELx_CV);
>> +ESR_DECLARE_CHECK_FUNC(dabt_valid, ESR_ELx_ISV);
>> +ESR_DECLARE_CHECK_FUNC(dabt_sse, ESR_ELx_SSE);
>> +ESR_DECLARE_CHECK_FUNC(dabt_sf, ESR_ELx_SF);
>> +ESR_DECLARE_CHECK_FUNC(dabt_s1ptw, ESR_ELx_S1PTW);
>> +ESR_DECLARE_CHECK_FUNC(dabt_write, ESR_ELx_WNR);
>> +ESR_DECLARE_CHECK_FUNC(dabt_cm, ESR_ELx_CM);
>> +
>> +ESR_DECLARE_GET_FUNC(class, ESR_ELx_EC_MASK, ESR_ELx_EC_SHIFT);
>> +ESR_DECLARE_GET_FUNC(fault, ESR_ELx_FSC, 0);
>> +ESR_DECLARE_GET_FUNC(fault_type, ESR_ELx_FSC_TYPE, 0);
>> +ESR_DECLARE_GET_FUNC(condition, ESR_ELx_COND_MASK, ESR_ELx_COND_SHIFT);
>> +ESR_DECLARE_GET_FUNC(hvc_imm, ESR_ELx_xVC_IMM_MASK, 0);
>> +ESR_DECLARE_GET_FUNC(dabt_iss_nisv_sanitized,
>> + (ESR_ELx_CM | ESR_ELx_WNR | ESR_ELx_FSC), 0);
>> +ESR_DECLARE_GET_FUNC(dabt_rd, ESR_ELx_SRT_MASK, ESR_ELx_SRT_SHIFT);
>> +ESR_DECLARE_GET_FUNC(dabt_as, ESR_ELx_SAS, ESR_ELx_SAS_SHIFT);
>> +ESR_DECLARE_GET_FUNC(sys_rt, ESR_ELx_SYS64_ISS_RT_MASK,
>> + ESR_ELx_SYS64_ISS_RT_SHIFT);
>
> I'm really not keen on this, as I think it's abstracting the problem at
> the wrong level, hiding information and making things harder to reason
> about rather than abstracting that.
>
> I strongly suspect the right thing to do is use FIELD_GET() in-place in
> the functions below, e.g.
>
> !!FIELD_GET(esr, ESR_ELx_IL);
>
> ... rather than:
>
> esr_get_il_32bit(esr);
>
> ... as that avoids the wrapper entirely, minimizing indirection and
> making the codebase simpler to navigate.
>
> For the cases where we *really* want a helper, i'd rather write those
> out explicitly, e.g.
>
It will be no difference except to use FIELD_GET() to make the code
more explicit. Maybe I didn't fully understand your comments here.
Please let me know if something like below is what you expect?
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index c9ba0df47f7d..e8294edcd8f4 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -343,7 +343,7 @@ static __always_inline unsigned int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *
/* This one is not specific to Data Abort */
static __always_inline bool kvm_vcpu_trap_il_is32bit(const struct kvm_vcpu *vcpu)
{
- return !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_IL);
+ return !!FIELD_GET(kvm_vcpu_get_esr(vcpu), ESR_ELx_IL);
}
If my understanding is correct, I think we needn't change the code
and this patch can be dropped.
> #define esr_get_hvc_imm(esr) FIELD_GET(esr, ESR_ELx_xVC_IMM_MASK)
>
> ... but I'm not sure if we really need those given these are mostly used
> *once* below.
>
We don't need these for now, but will be needed when the next revision
of async page fault is posted. Lets ignore this requirement for now
because I can revisit it when the async page fault patchset is posted.
That time, we can have accessors defined in esr.h and helpers in
kvm_emulate.h use those accessors. It's similar to what you're suggesting.
#define esr_get_hvc_imm(esr) FIELD_GET(esr, ESR_ELx_xVC_IMM_MASK)
static inline u32 kvm_vcpu_hvc_get_imm(const struct kvm_vcpu *vcpu)
{
return esr_get_hvc_imm(kvm_vcpu_get_esr(vcpu));
}
By the way, it's long way to reach that point because I'm still in the
middle of working on virtualizing SDEI currently.
>> +
>> const char *esr_get_class_string(u32 esr);
>> #endif /* __ASSEMBLY */
>>
>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>> index c9ba0df47f7d..9337d90c517f 100644
>> --- a/arch/arm64/include/asm/kvm_emulate.h
>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>> @@ -266,12 +266,8 @@ static __always_inline u32 kvm_vcpu_get_esr(const struct kvm_vcpu *vcpu)
>>
>> static __always_inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
>> {
>> - u32 esr = kvm_vcpu_get_esr(vcpu);
>> -
>> - if (esr & ESR_ELx_CV)
>> - return (esr & ESR_ELx_COND_MASK) >> ESR_ELx_COND_SHIFT;
>> -
>> - return -1;
>> + return esr_is_condition(kvm_vcpu_get_esr(vcpu)) ?
>> + esr_get_condition(kvm_vcpu_get_esr(vcpu)) : -1;
>> }
>
> Do we really need to change the structure of this code? I thought this
> was purely about decooupling helpers from the vcpu struct. This could
> have stayed as:
>
> static __always_inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
> {
> u32 esr = kvm_vcpu_get_esr(vcpu);
>
> if (esr_is_condition(esr))
> return esr_get_condition(esr);
>
> return -1;
> }
>
> ... or:
>
> static __always_inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
> {
> u32 esr = kvm_vcpu_get_esr(vcpu);
>
> if (FEILD_GET(esr, ESR_ELx_CV))
> return FIELD_GET(esr, ESR_ELx_COND_MASK);
>
> return -1;
> }
>
It's not needed to change the structure of the code, but it does
reduce the lines of codes. It's kind of my personal taste :)
[...]
Thanks,
Gavin
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