linux-kernel - Re: [PATCH 6/7] iommu/vt-d: Add helper to flush caches for context change

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Message-ID: <20240814162726.5efe1a6e.alex.williamson@redhat.com>
Date: Wed, 14 Aug 2024 16:27:26 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, Jacob Pan
 <jacob.jun.pan@...ux.intel.com>, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] iommu/vt-d: Add helper to flush caches for context
 change


Hi Baolu,

This appears to be non-functional and breaks device assignment...

On Tue,  2 Jul 2024 21:08:38 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 1f0d6892a0b6..e84b0fdca107 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
...
> @@ -1959,7 +1944,6 @@ static void domain_context_clear_one(struct device_domain_info *info, u8 bus, u8
>  {
>  	struct intel_iommu *iommu = info->iommu;
>  	struct context_entry *context;
> -	u16 did_old;
>  
>  	spin_lock(&iommu->lock);
>  	context = iommu_context_addr(iommu, bus, devfn, 0);
> @@ -1968,24 +1952,10 @@ static void domain_context_clear_one(struct device_domain_info *info, u8 bus, u8
>  		return;
>  	}
>  
> -	did_old = context_domain_id(context);
> -

    static inline int context_domain_id(struct context_entry *c)
    {
            return((c->hi >> 8) & 0xffff);
    }

>  	context_clear_entry(context);

    static inline void context_clear_entry(struct context_entry *context)
    {       
            context->lo = 0;
            context->hi = 0;
    }

>  	__iommu_flush_cache(iommu, context, sizeof(*context));
>  	spin_unlock(&iommu->lock);
> -	iommu->flush.flush_context(iommu,
> -				   did_old,
> -				   (((u16)bus) << 8) | devfn,
> -				   DMA_CCMD_MASK_NOBIT,
> -				   DMA_CCMD_DEVICE_INVL);
> -
> -	iommu->flush.flush_iotlb(iommu,
> -				 did_old,
> -				 0,
> -				 0,
> -				 DMA_TLB_DSI_FLUSH);
> -
> -	__iommu_flush_dev_iotlb(info, 0, MAX_AGAW_PFN_WIDTH);
> +	intel_context_flush_present(info, context, true);
>  }
>  
>  static int domain_setup_first_level(struct intel_iommu *iommu,
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index aabcdf756581..d6623d2c2050 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
...
> +void intel_context_flush_present(struct device_domain_info *info,
> +				 struct context_entry *context,
> +				 bool flush_domains)
> +{
> +	struct intel_iommu *iommu = info->iommu;
> +	u16 did = context_domain_id(context);

Whoops, did is always zero here, intel_context_flush_present() precedes
all callers.

> +	struct pasid_entry *pte;
> +	int i;
> +
> +	/*
> +	 * Device-selective context-cache invalidation. The Domain-ID field
> +	 * of the Context-cache Invalidate Descriptor is ignored by hardware
> +	 * when operating in scalable mode. Therefore the @did value doesn't
> +	 * matter in scalable mode.
> +	 */
> +	iommu->flush.flush_context(iommu, did, PCI_DEVID(info->bus, info->devfn),
                                          ^^^ Bogus
> +				   DMA_CCMD_MASK_NOBIT, DMA_CCMD_DEVICE_INVL);
> +
> +	/*
> +	 * For legacy mode:
> +	 * - Domain-selective IOTLB invalidation
> +	 * - Global Device-TLB invalidation to all affected functions
> +	 */
> +	if (!sm_supported(iommu)) {
> +		iommu->flush.flush_iotlb(iommu, did, 0, 0, DMA_TLB_DSI_FLUSH);
                                                ^^^ etc...
> +		__context_flush_dev_iotlb(info);
> +
> +		return;
> +	}

Thanks,
Alex