On Tue, Jun 30, 2020 at 10:16:07AM +1000, Gavin Shan wrote:
> 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@xxxxxxxxxx>
> >
> > 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?
Sorry; my point here was just that using FIELD_GET() explicitly was
preferable to generating an entire function with
ESR_DECLARE_CHECK_FUNC() if the goal was just to remove the explciit
mask-and-shift at each callsite.
I agree they'd have the same functional behaviour, but I think the
explicit FIELD_GET() approach is easier to read (and possible to search
for), which makes code maintenance much easier.
> 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.
If you don't see a need for a change, I'm also happy for this to 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));
> }
That'd be fine by me.
Thanks,
Mark.
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