linux-kernel - RE: [PATCH 02/12] iommu/vt-d: Add cache tag invalidation helpers

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Date: Thu, 28 Mar 2024 07:39:32 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...pe.ca>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "Liu, Yi L" <yi.l.liu@...el.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 02/12] iommu/vt-d: Add cache tag invalidation helpers

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Monday, March 25, 2024 10:17 AM
> 
> +
> +static unsigned long calculate_psi_aligned_address(unsigned long start,
> +						   unsigned long end,
> +						   unsigned long *_pages,
> +						   unsigned long *_mask)
> +{
> +	unsigned long pages = (end - start + VTD_PAGE_SIZE - 1) >>
> VTD_PAGE_SHIFT;

this doesn't sound correct. You'd want to follow aligned_nrpages().

> +		case CACHE_TAG_TYPE_DEVTLB:
> +			if (tag->pasid == IOMMU_NO_PASID)
> +				qi_flush_dev_iotlb(iommu, sid, info->pfsid,
> +						   info->ats_qdep, addr,
> mask);
> +			else
> +				qi_flush_dev_iotlb_pasid(iommu, sid, info-
> >pfsid,
> +							 tag->pasid, info-
> >ats_qdep,
> +							 addr, mask);
> +
> +			quirk_extra_dev_tlb_flush(info, addr, mask, tag-
> >pasid, info->ats_qdep);
> +			break;
> +		case CACHE_TAG_TYPE_PARENT_DEVTLB:
> +			/*
> +			 * Address translation cache in device side caches the
> +			 * result of nested translation. There is no easy way
> +			 * to identify the exact set of nested translations
> +			 * affected by a change in S2. So just flush the entire
> +			 * device cache.
> +			 */
> +			qi_flush_dev_iotlb(iommu, sid, info->pfsid, info-
> >ats_qdep,
> +					   0, MAX_AGAW_PFN_WIDTH);
> +			quirk_extra_dev_tlb_flush(info, 0,
> MAX_AGAW_PFN_WIDTH,
> +						  IOMMU_NO_PASID, info-
> >ats_qdep);
> +			break;

parent devtlb can has pasid too, though not enabled now. As core helpers
probably we can support it now leading to simpler code:

	case CACHE_TAG_TYPE_PARENT_DEVTLB:
		//change addr/mask
		//fallthrough
	case CACHE_TAG_TYPE_DEVTLB:
		//what this patch does

> +void cache_tag_flush_all(struct dmar_domain *domain)
> +{
> +	struct cache_tag *tag;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&domain->cache_lock, flags);
> +	list_for_each_entry(tag, &domain->cache_tags, node) {
> +		struct device_domain_info *info = dev_iommu_priv_get(tag-
> >dev);
> +		struct intel_iommu *iommu = tag->iommu;
> +		u16 sid = PCI_DEVID(info->bus, info->devfn);
> +
> +		switch (tag->type) {
> +		case CACHE_TAG_TYPE_IOTLB:
> +		case CACHE_TAG_TYPE_PARENT_IOTLB:
> +			if (domain->use_first_level)
> +				qi_flush_piotlb(iommu, tag->domain_id,
> +						tag->pasid, 0, -1, 0);
> +			else
> +				iommu->flush.flush_iotlb(iommu, tag-
> >domain_id,
> +							 0, 0,
> DMA_TLB_DSI_FLUSH);
> +			break;
> +		case CACHE_TAG_TYPE_DEVTLB:
> +		case CACHE_TAG_TYPE_PARENT_DEVTLB:
> +			qi_flush_dev_iotlb(iommu, sid, info->pfsid, info-
> >ats_qdep,
> +					   0, MAX_AGAW_PFN_WIDTH);
> +			quirk_extra_dev_tlb_flush(info, 0,
> MAX_AGAW_PFN_WIDTH,
> +						  IOMMU_NO_PASID, info-
> >ats_qdep);
> +			break;
> +		}
> +	}

could this loop be consolidated with the one in previous helper? anyway
the only difference is on addr/mask...

> +/*
> + * Invalidate a range of IOVA when IOMMU is in caching mode and new
> mappings
> + * are added to the target domain.
> + */
> +void cache_tag_flush_cm_range(struct dmar_domain *domain, unsigned
> long start,
> +			      unsigned long end)
> +{

I'm also not sure why this is worth a separate helper. why couldn't it
be managed by previous flush_range()? 

> +	unsigned long pages, mask, addr;
> +	struct cache_tag *tag;
> +	unsigned long flags;
> +
> +	addr = calculate_psi_aligned_address(start, end, &pages, &mask);
> +
> +	spin_lock_irqsave(&domain->cache_lock, flags);
> +	list_for_each_entry(tag, &domain->cache_tags, node) {
> +		struct intel_iommu *iommu = tag->iommu;
> +
> +		/*
> +		 * When IOMMU is enabled in caching mode some non-
> present
> +		 * mappings may be cached by the IOTLB if it uses second-
> +		 * only translation.
> +		 */
> +		if (!cap_caching_mode(iommu->cap) || domain-
> >use_first_level) {
> +			iommu_flush_write_buffer(iommu);
> +			continue;
> +		}

the comment really doesn't tell what this block does. from its intention
it probably more suitable to be in the caller side as today.

> +
> +		if (tag->type == CACHE_TAG_TYPE_IOTLB ||
> +		    tag->type == CACHE_TAG_TYPE_PARENT_IOTLB) {
> +			/*
> +			 * Fallback to domain selective flush if no
> +			 * PSI support or the size is too big.
> +			 */
> +			if (!cap_pgsel_inv(iommu->cap) ||
> +			    mask > cap_max_amask_val(iommu->cap))
> +				iommu->flush.flush_iotlb(iommu, tag-
> >domain_id,
> +							 0, 0,
> DMA_TLB_DSI_FLUSH);
> +			else
> +				iommu->flush.flush_iotlb(iommu, tag-
> >domain_id,
> +							 addr, mask,
> +
> DMA_TLB_PSI_FLUSH);
> +		}
> +	}

You skipped devtlb invalidation. yes it's not necessary based on current
nested translation design and this part is inconsistent in different paths.

but as a semantics change you may want to first make removing devtlb
invalidation a separate patch and then do this cleanup, so bisect is easier.