Re: [PATCH 4/4] iommu/vt-d: Remove lazy allocation of domains

[Lu Baolu]

Hi,

On 3/5/19 7:46 PM, James Sewart wrote:
> Hey Lu,
>
> > On 5 Mar 2019, at 06:59, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > It's hard for me to understand why do we remove the rmrr related
> > code in this patch.
>
> The RMRR code removed here requires the lazy allocation of domains to
> exist, as it is run before iommu.c would assign IOMMU groups and attach a
> domain. Before patch 3, removing this code would mean the RMRR regions are
> never mapped for a domain: iommu.c will allocate a default domain for the
> group that a device is about to be put in, it will attach the domain to
> the device, then for each region returned by get_resv_regions it will
> create an identity map, this is where the RMRRs are setup for the default
> domain. >
> > And, now we have two places to hold a domain for a device: group and
> > dev->info. We can consider to optimize the use of per device iommu
> > arch data. This should be later work anyway.
> >
> > More comments inline.
> >
> > On 3/4/19 11:47 PM, James Sewart wrote:
> > > The generic IOMMU code will allocate and attach a dma ops domain to each
> > > device that comes online, replacing any lazy allocated domain. Removes
> > > RMRR application at iommu init time as we won't have a domain attached
> > > to any device. iommu.c will do this after attaching a device using
> > > create_direct_mappings.
> > > Signed-off-by: James Sewart <jamessewart@xxxxxxxxxx>
> > > ---
> > >   drivers/iommu/intel-iommu.c | 202 ++----------------------------------
> > >   1 file changed, 8 insertions(+), 194 deletions(-)
> > > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > > index 71cd6bbfec05..282257e2628d 100644
> > > --- a/drivers/iommu/intel-iommu.c
> > > +++ b/drivers/iommu/intel-iommu.c
> > > @@ -2595,118 +2595,6 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
> > >   	return domain;
> > >   }
> > >   -static int get_last_alias(struct pci_dev *pdev, u16 alias, void *opaque)
> > > -{
> > > -	*(u16 *)opaque = alias;
> > > -	return 0;
> > > -}
> > > -
> > > -static struct dmar_domain *find_or_alloc_domain(struct device *dev, int gaw)
> > > -{
> > > -	struct device_domain_info *info = NULL;
> > > -	struct dmar_domain *domain = NULL;
> > > -	struct intel_iommu *iommu;
> > > -	u16 dma_alias;
> > > -	unsigned long flags;
> > > -	u8 bus, devfn;
> > > -
> > > -	iommu = device_to_iommu(dev, &bus, &devfn);
> > > -	if (!iommu)
> > > -		return NULL;
> > > -
> > > -	if (dev_is_pci(dev)) {
> > > -		struct pci_dev *pdev = to_pci_dev(dev);
> > > -
> > > -		pci_for_each_dma_alias(pdev, get_last_alias, &dma_alias);
> > > -
> > > -		spin_lock_irqsave(&device_domain_lock, flags);
> > > -		info = dmar_search_domain_by_dev_info(pci_domain_nr(pdev->bus),
> > > -						      PCI_BUS_NUM(dma_alias),
> > > -						      dma_alias & 0xff);
> > > -		if (info) {
> > > -			iommu = info->iommu;
> > > -			domain = info->domain;
> > > -		}
> > > -		spin_unlock_irqrestore(&device_domain_lock, flags);
> > > -
> > > -		/* DMA alias already has a domain, use it */
> > > -		if (info)
> > > -			goto out;
> > > -	}
> > > -
> > > -	/* Allocate and initialize new domain for the device */
> > > -	domain = alloc_domain(0);
> > > -	if (!domain)
> > > -		return NULL;
> > > -	if (domain_init(domain, iommu, gaw)) {
> > > -		domain_exit(domain);
> > > -		return NULL;
> > > -	}
> > > -
> > > -out:
> > > -
> > > -	return domain;
> > > -}
> > > -
> > > -static struct dmar_domain *set_domain_for_dev(struct device *dev,
> > > -					      struct dmar_domain *domain)
> > > -{
> > > -	struct intel_iommu *iommu;
> > > -	struct dmar_domain *tmp;
> > > -	u16 req_id, dma_alias;
> > > -	u8 bus, devfn;
> > > -
> > > -	iommu = device_to_iommu(dev, &bus, &devfn);
> > > -	if (!iommu)
> > > -		return NULL;
> > > -
> > > -	req_id = ((u16)bus << 8) | devfn;
> > > -
> > > -	if (dev_is_pci(dev)) {
> > > -		struct pci_dev *pdev = to_pci_dev(dev);
> > > -
> > > -		pci_for_each_dma_alias(pdev, get_last_alias, &dma_alias);
> > > -
> > > -		/* register PCI DMA alias device */
> > > -		if (req_id != dma_alias) {
> > > -			tmp = dmar_insert_one_dev_info(iommu, PCI_BUS_NUM(dma_alias),
> > > -					dma_alias & 0xff, NULL, domain);
> > > -
> > > -			if (!tmp || tmp != domain)
> > > -				return tmp;
> > > -		}
> > > -	}
> > > -
> > > -	tmp = dmar_insert_one_dev_info(iommu, bus, devfn, dev, domain);
> > > -	if (!tmp || tmp != domain)
> > > -		return tmp;
> > > -
> > > -	return domain;
> > > -}
> > > -
> > > -static struct dmar_domain *get_domain_for_dev(struct device *dev, int gaw)
> > > -{
> > > -	struct dmar_domain *domain, *tmp;
> > > -
> > > -	domain = find_domain(dev);
> > > -	if (domain)
> > > -		goto out;
> > > -
> > > -	domain = find_or_alloc_domain(dev, gaw);
> > > -	if (!domain)
> > > -		goto out;
> > > -
> > > -	tmp = set_domain_for_dev(dev, domain);
> > > -	if (!tmp || domain != tmp) {
> > > -		domain_exit(domain);
> > > -		domain = tmp;
> > > -	}
> > > -
> > > -out:
> > > -
> > > -	return domain;
> > > -}
> > > -
> > >   static int iommu_domain_identity_map(struct dmar_domain *domain,
> > >   				     unsigned long long start,
> > >   				     unsigned long long end)
> > > @@ -2779,7 +2667,7 @@ static int iommu_prepare_identity_map(struct device *dev,
> > >   	struct dmar_domain *domain;
> > >   	int ret;
> > >   -	domain = get_domain_for_dev(dev, DEFAULT_DOMAIN_ADDRESS_WIDTH);
> > > +	domain = find_domain(dev);
> > >   	if (!domain)
> > >   		return -ENOMEM;
> > >   @@ -3301,11 +3189,9 @@ static int copy_translation_tables(struct intel_iommu *iommu)
> > >   static int __init init_dmars(void)
> > >   {
> > >   	struct dmar_drhd_unit *drhd;
> > > -	struct dmar_rmrr_unit *rmrr;
> > >   	bool copied_tables = false;
> > > -	struct device *dev;
> > >   	struct intel_iommu *iommu;
> > > -	int i, ret;
> > > +	int ret;
> > >     	/*
> > >   	 * for each drhd
> > > @@ -3466,32 +3352,6 @@ static int __init init_dmars(void)
> > >   			goto free_iommu;
> > >   		}
> > >   	}
> > > -	/*
> > > -	 * For each rmrr
> > > -	 *   for each dev attached to rmrr
> > > -	 *   do
> > > -	 *     locate drhd for dev, alloc domain for dev
> > > -	 *     allocate free domain
> > > -	 *     allocate page table entries for rmrr
> > > -	 *     if context not allocated for bus
> > > -	 *           allocate and init context
> > > -	 *           set present in root table for this bus
> > > -	 *     init context with domain, translation etc
> > > -	 *    endfor
> > > -	 * endfor
> > > -	 */
> > > -	pr_info("Setting RMRR:\n");
> > > -	for_each_rmrr_units(rmrr) {
> > > -		/* some BIOS lists non-exist devices in DMAR table. */
> > > -		for_each_active_dev_scope(rmrr->devices, rmrr->devices_cnt,
> > > -					  i, dev) {
> > > -			ret = iommu_prepare_rmrr_dev(rmrr, dev);
> > > -			if (ret)
> > > -				pr_err("Mapping reserved region failed\n");
> > > -		}
> > > -	}
> > > -
> > > -	iommu_prepare_isa();
> >
> > Why do you want to remove this segment of code?
>
> This will only work if the lazy allocation of domains exists, these
> mappings will disappear once a default domain is attached to a device and
> then remade by iommu_group_create_direct_mappings. This code is redundant
> and removing it allows us to remove all the lazy allocation logic.

No exactly.

We need to setup the rmrr mapping before enabling dma remapping,
otherwise, there will be a window after dma remapping enabling and
rmrr getting mapped, during which people might see dma faults.

> iommu_prepare_isa does need moving to get_resv_regions for its mappings to
> be applied, this will need some refactoring.

Yes, agree.

> > >     domains_done:
> > >   @@ -3580,53 +3440,6 @@ static unsigned long intel_alloc_iova(struct device *dev,
> > >   	return iova_pfn;
> > >   }
> > >   -struct dmar_domain *get_valid_domain_for_dev(struct device *dev)
> > > -{
> > > -	struct dmar_domain *domain, *tmp;
> > > -	struct dmar_rmrr_unit *rmrr;
> > > -	struct device *i_dev;
> > > -	int i, ret;
> > > -
> > > -	domain = find_domain(dev);
> > > -	if (domain)
> > > -		goto out;
> > > -
> > > -	domain = find_or_alloc_domain(dev, DEFAULT_DOMAIN_ADDRESS_WIDTH);
> > > -	if (!domain)
> > > -		goto out;
> > > -
> > > -	/* We have a new domain - setup possible RMRRs for the device */
> > > -	rcu_read_lock();
> > > -	for_each_rmrr_units(rmrr) {
> > > -		for_each_active_dev_scope(rmrr->devices, rmrr->devices_cnt,
> > > -					  i, i_dev) {
> > > -			if (i_dev != dev)
> > > -				continue;
> > > -
> > > -			ret = domain_prepare_identity_map(dev, domain,
> > > -							  rmrr->base_address,
> > > -							  rmrr->end_address);
> > > -			if (ret)
> > > -				dev_err(dev, "Mapping reserved region failed\n");
> >
> > We can't simply remove this segment of code, right? At least it should
> > be moved to the domain allocation interface.
>
> iommu_group_create_direct_mappings will take care of these mappings, this
> code is not used once an externally managed domain(group domain) is
> attached to the device.

Yes, this seems to be duplicated even with lazy domain allocation.

Best regards,
Lu Baolu

> > > -		}
> > > -	}
> > > -	rcu_read_unlock();
> > > -
> > > -	tmp = set_domain_for_dev(dev, domain);
> > > -	if (!tmp || domain != tmp) {
> > > -		domain_exit(domain);
> > > -		domain = tmp;
> > > -	}
> > > -
> > > -out:
> > > -
> > > -	if (!domain)
> > > -		pr_err("Allocating domain for %s failed\n", dev_name(dev));
> > > -
> > > -
> > > -	return domain;
> > > -}
> > > -
> > >   /* Check if the dev needs to go through non-identity map and unmap process.*/
> > >   static int iommu_no_mapping(struct device *dev)
> > >   {
> > > @@ -3689,7 +3502,7 @@ static dma_addr_t __intel_map_page(struct device *dev, struct page *page,
> > >   	if (iommu_no_mapping(dev))
> > >   		return paddr;
> > >   -	domain = get_valid_domain_for_dev(dev);
> > > +	domain = find_domain(dev);
> > >   	if (!domain)
> > >   		return DMA_MAPPING_ERROR;
> > >   @@ -3753,7 +3566,8 @@ static void intel_unmap(struct device *dev, dma_addr_t dev_addr, size_t size)
> > >   		return;
> > >     	domain = find_domain(dev);
> > > -	BUG_ON(!domain);
> > > +	if (!domain)
> > > +		return;
> > >   
> >
> > This is not related to this patch. Let's do it in a separated patch.
> >
> > >   	iommu = domain_get_iommu(domain);
> > >   @@ -3899,7 +3713,7 @@ static int intel_map_sg(struct device *dev, struct scatterlist *sglist, int nele
> > >   	if (iommu_no_mapping(dev))
> > >   		return intel_nontranslate_map_sg(dev, sglist, nelems, dir);
> > >   -	domain = get_valid_domain_for_dev(dev);
> > > +	domain = find_domain(dev);
> > >   	if (!domain)
> > >   		return 0;
> > >   @@ -5377,9 +5191,9 @@ int intel_iommu_enable_pasid(struct intel_iommu *iommu, struct intel_svm_dev *sd
> > >   	u64 ctx_lo;
> > >   	int ret;
> > >   -	domain = get_valid_domain_for_dev(sdev->dev);
> > > +	domain = find_domain(sdev->dev);
> > >   	if (!domain)
> > > -		return -EINVAL;
> > > +		return -ENOMEM;
> >
> > This is not related to this patch. Let's do it in a separated patch.
> >
> > >     	spin_lock_irqsave(&device_domain_lock, flags);
> > >   	spin_lock(&iommu->lock);
> >
> > Best regards,
> > Lu Baolu