linux-kernel - Re: [PATCH v3 1/8] iommu/vt-d: Fix CPU and IOMMU SVM feature matching checks

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Date:   Wed, 20 Nov 2019 21:59:30 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>
Subject: Re: [PATCH v3 1/8] iommu/vt-d: Fix CPU and IOMMU SVM feature matching
 checks

Hi Jacob,

On 11/19/19 6:56 PM, Jacob Pan wrote:
> Shared Virtual Memory(SVM) is based on a collective set of hardware
> features detected at runtime. There are requirements for matching CPU
> and IOMMU capabilities.
> 
> 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. The consequences can be:
> 1. CPU uses 5-level paging mode for virtual address of 57 bits, but
> IOMMU can only support 4-level paging mode with 48 bits address for DMA.
> 2. 1GB page size is used by CPU but IOMMU does not support it. VT-d
> unrecoverable faults may be generated.
> 
> The best solution to fix these problems is to prevent them in the first
> place.
> 
> This patch consolidates code for checking PASID, CPU vs. IOMMU paging
> mode compatibility, as well as provides specific error messages for
> each failed checks. On sane hardware configurations, these error message
> shall never appear in kernel log.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Acked-by: Lu Baolu <baolu.lu@...ux.intel.com>
Reviewed-by: Eric Auger <eric.auger@...hat.com>

Thanks

Eric
> ---
>  drivers/iommu/intel-iommu.c | 10 ++--------
>  drivers/iommu/intel-svm.c   | 40 +++++++++++++++++++++++++++-------------
>  include/linux/intel-iommu.h |  5 ++++-
>  3 files changed, 33 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);
> +		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 ed11ef594378..7dcfa1c4a844 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -433,6 +433,7 @@ enum {
>  
>  #define VTD_FLAG_TRANS_PRE_ENABLED	(1 << 0)
>  #define VTD_FLAG_IRQ_REMAP_PRE_ENABLED	(1 << 1)
> +#define VTD_FLAG_SVM_CAPABLE		(1 << 2)
>  
>  extern int intel_iommu_sm;
>  
> @@ -656,7 +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);
>  
> @@ -684,6 +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
>