Re: [PATCH v2 3/7] iommu/vt-d: Expose ISA direct mapping region via iommu_get_resv_regions

[Lu Baolu]

Hi James,

On 3/22/19 5:57 PM, James Sewart wrote:
> Hey Lu,
>
> > On 15 Mar 2019, at 02:19, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
> >
> > Hi James,
> >
> > On 3/14/19 7:58 PM, James Sewart wrote:
> > > To support mapping ISA region via iommu_group_create_direct_mappings,
> > > make sure its exposed by iommu_get_resv_regions. This allows
> > > deduplication of reserved region mappings
> > > Signed-off-by: James Sewart <jamessewart@xxxxxxxxxx>
> > > ---
> > >   drivers/iommu/intel-iommu.c | 42 +++++++++++++++++++++++++++++--------
> > >   1 file changed, 33 insertions(+), 9 deletions(-)
> > > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > > index 8e0a4e2ff77f..2e00e8708f06 100644
> > > --- a/drivers/iommu/intel-iommu.c
> > > +++ b/drivers/iommu/intel-iommu.c
> > > @@ -337,6 +337,8 @@ static LIST_HEAD(dmar_rmrr_units);
> > >   #define for_each_rmrr_units(rmrr) \
> > >   	list_for_each_entry(rmrr, &dmar_rmrr_units, list)
> > >   +static struct iommu_resv_region *isa_resv_region;
> > > +
> > >   /* bitmap for indexing intel_iommus */
> > >   static int g_num_of_iommus;
> > >   @@ -2780,26 +2782,34 @@ static inline int iommu_prepare_rmrr_dev(struct dmar_rmrr_unit *rmrr,
> > >   					  rmrr->end_address);
> > >   }
> > >   +static inline struct iommu_resv_region *iommu_get_isa_resv_region(void)
> > > +{
> > > +	if (!isa_resv_region)
> > > +		isa_resv_region = iommu_alloc_resv_region(0,
> > > +				16*1024*1024,
> > > +				0, IOMMU_RESV_DIRECT);
> > > +
> > > +	return isa_resv_region;
> > > +}
> > > +
> > >   #ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
> > > -static inline void iommu_prepare_isa(void)
> > > +static inline void iommu_prepare_isa(struct pci_dev *pdev)
> > >   {
> > > -	struct pci_dev *pdev;
> > >   	int ret;
> > > +	struct iommu_resv_region *reg = iommu_get_isa_resv_region();
> > >   -	pdev = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> > > -	if (!pdev)
> > > +	if (!reg)
> > >   		return;
> > >     	pr_info("Prepare 0-16MiB unity mapping for LPC\n");
> > > -	ret = iommu_prepare_identity_map(&pdev->dev, 0, 16*1024*1024 - 1);
> > > +	ret = iommu_prepare_identity_map(&pdev->dev, reg->start,
> > > +			reg->start + reg->length - 1);
> > >     	if (ret)
> > >   		pr_err("Failed to create 0-16MiB identity map - floppy might not work\n");
> > > -
> > > -	pci_dev_put(pdev);
> > >   }
> > >   #else
> > > -static inline void iommu_prepare_isa(void)
> > > +static inline void iommu_prepare_isa(struct pci_dev *pdev)
> > >   {
> > >   	return;
> > >   }
> > > @@ -3289,6 +3299,7 @@ static int __init init_dmars(void)
> > >   	struct dmar_rmrr_unit *rmrr;
> > >   	bool copied_tables = false;
> > >   	struct device *dev;
> > > +	struct pci_dev *pdev;
> > >   	struct intel_iommu *iommu;
> > >   	int i, ret;
> > >   @@ -3469,7 +3480,11 @@ static int __init init_dmars(void)
> > >   		}
> > >   	}
> > >   -	iommu_prepare_isa();
> > > +	pdev = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
> > > +	if (pdev) {
> > > +		iommu_prepare_isa(pdev);
> > > +		pci_dev_put(pdev);
> > > +	}
> > >     domains_done:
> > >   @@ -5266,6 +5281,7 @@ static void intel_iommu_get_resv_regions(struct device *device,
> > >   	struct iommu_resv_region *reg;
> > >   	struct dmar_rmrr_unit *rmrr;
> > >   	struct device *i_dev;
> > > +	struct pci_dev *pdev;
> > >   	int i;
> > >     	rcu_read_lock();
> > > @@ -5280,6 +5296,14 @@ static void intel_iommu_get_resv_regions(struct device *device,
> > >   	}
> > >   	rcu_read_unlock();
> > >   +	if (dev_is_pci(device)) {
> > > +		pdev = to_pci_dev(device);
> > > +		if ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA) {
> > > +			reg = iommu_get_isa_resv_region();
> > > +			list_add_tail(&reg->list, head);
> > > +		}
> > > +	}
> > > +
> >
> > Just wondering why not just
> >
> > +#ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
> > +	if (dev_is_pci(device)) {
> > +		pdev = to_pci_dev(device);
> > +		if ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA) {
> > +			reg = iommu_alloc_resv_region(0,
> > +				16*1024*1024,
> > +				0, IOMMU_RESV_DIRECT);
> > +			if (reg)
> > +				list_add_tail(&reg->list, head);
> > +		}
> > +	}
> > +#endif
> >
> > and, remove all other related code?
>
> At this point in the patchset if we remove iommu_prepare_isa then the ISA
> region wonât be mapped to the device. Only once the dma domain is allocable
> will the reserved regions be mapped by iommu_group_create_direct_mappings.

Yes. So if we put the allocation code here, it won't impact anything and
will take effect as soon as the dma domain is allocatable.

> Theres an issue that if we choose to alloc a new resv_region with type
> IOMMU_RESV_DIRECT, we will need to refactor intel_iommu_put_resv_regions
> to free this entry type which means refactoring the rmrr regions in
> get_resv_regions. Should this work be in this patchset?

Do you mean the rmrr regions are not allocated in get_resv_regions, but
are freed in put_resv_regions? I think we should fix this in this patch
set since this might impact the device passthrough if we don't do it.

Best regards,
Lu Baolu