Hi, Peter,
On Fri, Jun 26, 2020 at 11:44:50AM +0200, Peter Zijlstra wrote:
> On Thu, Jun 25, 2020 at 01:17:22PM -0700, Fenghua Yu wrote:
>
> > +static bool fixup_pasid_exception(void)
> > +{
> > + if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> > + return false;
> > + if (!static_cpu_has(X86_FEATURE_ENQCMD))
> > + return false;
>
> elsewhere you had another variation:
>
> + if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> + return;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> + return;
>
> Which is it, and why do we need the CONFIG thing when combined with the
> enabled thing?
>
I will use the second one with cpu_feature_enabled() for both cases.
The CONFIG thing is for compilation time optimization when
CONFIG_INTEL_IOMMU_SVM is not set.
If CONFIG_INTEL_IOMMU_SVM is not set, IS_ENABLED(CONFIG_INTEL_IOMMU_SVM)
is "false" during compilation time. Then GCC will optimize
fixup_pasid_execption() to empty and will not define
__fixup_pasid_exception() at all because no one calls it.
If CONFIG_INTEL_IOMMU_SVM is set, IS_ENABLED(...) is always true.
Depending on cpu_feature_enabled(X86_FEATURE_ENQCMD), __fixup_pasid_execption()
will be called or not during run time.
Does it make sense?
Do you want me to define a helper enqcmd_enabled()?
static inline bool enqcmd_enabled(void)
{
if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
return false;
if (!static_cpu_has(X86_FEATURE_ENQCMD))
return false;
return true;
}
Then both fixup_pasid_execption() and free_pasid() can call it.
static bool fixup_pasid_exception(void)
{
if (!enqcmd_enabled())
return false;
return __fixup_pasid_exception();
}
statis inline void free_pasid(struct m_struct *mm)
{
if (!enqcmd_enabled())
return;
__free_pasid(mm);
}
Please advice.
-Fenghua
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