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

[Lu Baolu <baolu.lu@linux.intel.com>]

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@linux.intel.com> 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@arista.com>
>>> ---
>>>   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 won’t 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