Re: [PATCH v2 02/10] iommu/vt-d: Fix CPU and IOMMU SVM feature matching checks

[Jacob Pan]

On Mon, 18 Nov 2019 21:33:34 +0100
Auger Eric <eric.auger@xxxxxxxxxx> wrote:

> Hi Jacob,
> 
> On 11/18/19 8:42 PM, Jacob Pan wrote:
> > The current code checks CPU and IOMMU feature set for SVM support
> > but the result is never stored nor used. Therefore, SVM can still
> > be used even when these checks failed.  
> "SVM can still be used even when these checks failed". What were the
> consequences if it happened? Does it fix this cleanly now.
> > 
The consequence is DMA cannot reach above 48-bit virtual address range
when CPU does 5-level and IOMMU can only do 4-level. With is fix,
svm_bind_mm will fail in the first place to prevent SVM use by DMA.

> > This patch consolidates code for checking PASID, CPU vs. IOMMU
> > paging mode compatibility, as well as provides specific error
> > messages for each failed checks.>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > Acked-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/intel-iommu.c | 10 ++--------
> >  drivers/iommu/intel-svm.c   | 40
> > +++++++++++++++++++++++++++-------------
> > include/linux/intel-iommu.h |  4 +++- 3 files changed, 32
> > insertions(+), 22 deletions(-)
> > 
> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 3f974919d3bd..d598168e410d
> > 100644 --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -3289,10 +3289,7 @@ static int __init init_dmars(void)
> >  
> >  		if (!ecap_pass_through(iommu->ecap))
> >  			hw_pass_through = 0;
> > -#ifdef CONFIG_INTEL_IOMMU_SVM
> > -		if (pasid_supported(iommu))
> > -			intel_svm_init(iommu);
> > -#endif
> > +		intel_svm_check(iommu);
> >  	}
> >  
> >  	/*
> > @@ -4471,10 +4468,7 @@ static int intel_iommu_add(struct
> > dmar_drhd_unit *dmaru) if (ret)
> >  		goto out;
> >  
> > -#ifdef CONFIG_INTEL_IOMMU_SVM
> > -	if (pasid_supported(iommu))
> > -		intel_svm_init(iommu);
> > -#endif
> > +	intel_svm_check(iommu);
> >  
> >  	if (dmaru->ignored) {
> >  		/*
> > diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> > index 9b159132405d..716c543488f6 100644
> > --- a/drivers/iommu/intel-svm.c
> > +++ b/drivers/iommu/intel-svm.c
> > @@ -23,19 +23,6 @@
> >  
> >  static irqreturn_t prq_event_thread(int irq, void *d);
> >  
> > -int intel_svm_init(struct intel_iommu *iommu)
> > -{
> > -	if (cpu_feature_enabled(X86_FEATURE_GBPAGES) &&
> > -			!cap_fl1gp_support(iommu->cap))
> > -		return -EINVAL;
> > -
> > -	if (cpu_feature_enabled(X86_FEATURE_LA57) &&
> > -			!cap_5lp_support(iommu->cap))
> > -		return -EINVAL;
> > -
> > -	return 0;
> > -}
> > -
> >  #define PRQ_ORDER 0
> >  
> >  int intel_svm_enable_prq(struct intel_iommu *iommu)
> > @@ -99,6 +86,33 @@ int intel_svm_finish_prq(struct intel_iommu
> > *iommu) return 0;
> >  }
> >  
> > +static inline bool intel_svm_capable(struct intel_iommu *iommu)
> > +{
> > +	return iommu->flags & VTD_FLAG_SVM_CAPABLE;
> > +}
> > +
> > +void intel_svm_check(struct intel_iommu *iommu)
> > +{
> > +	if (!pasid_supported(iommu))
> > +		return;
> > +
> > +	if (cpu_feature_enabled(X86_FEATURE_GBPAGES) &&
> > +	    !cap_fl1gp_support(iommu->cap)) {
> > +		pr_err("%s SVM disabled, incompatible 1GB page
> > capability\n",
> > +		       iommu->name);  
> nit: is it really an error or just a warning?
I think it is an error in that there is an illegal configuration. It is
mostly for vIOMMU, we expect native HW should have these features
matched.

> > +		return;
> > +	}
> > +
> > +	if (cpu_feature_enabled(X86_FEATURE_LA57) &&
> > +	    !cap_5lp_support(iommu->cap)) {
> > +		pr_err("%s SVM disabled, incompatible paging
> > mode\n",
> > +		       iommu->name);
> > +		return;
> > +	}
> > +
> > +	iommu->flags |= VTD_FLAG_SVM_CAPABLE;
> > +}
> > +
> >  static void intel_flush_svm_range_dev (struct intel_svm *svm,
> > struct intel_svm_dev *sdev, unsigned long address, unsigned long
> > pages, int ih) {
> > diff --git a/include/linux/intel-iommu.h
> > b/include/linux/intel-iommu.h index 63118991824c..7dcfa1c4a844
> > 100644 --- a/include/linux/intel-iommu.h
> > +++ b/include/linux/intel-iommu.h
> > @@ -657,7 +657,7 @@ void iommu_flush_write_buffer(struct
> > intel_iommu *iommu); int intel_iommu_enable_pasid(struct
> > intel_iommu *iommu, struct device *dev); 
> >  #ifdef CONFIG_INTEL_IOMMU_SVM
> > -int intel_svm_init(struct intel_iommu *iommu);
> > +extern void intel_svm_check(struct intel_iommu *iommu);
> >  extern int intel_svm_enable_prq(struct intel_iommu *iommu);
> >  extern int intel_svm_finish_prq(struct intel_iommu *iommu);
> >  
> > @@ -685,6 +685,8 @@ struct intel_svm {
> >  };
> >  
> >  extern struct intel_iommu *intel_svm_device_to_iommu(struct device
> > *dev); +#else
> > +static inline void intel_svm_check(struct intel_iommu *iommu) {}
> >  #endif
> >  
> >  #ifdef CONFIG_INTEL_IOMMU_DEBUGFS
> >   
> Besides,
> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
> 
> Thanks
> 
> Eric
> 

[Jacob Pan]