Subject: Re: [RFC PATCH v3 3/5] PCI: Add host bridge attribute to indicate filtering of MSIs is supported

From: Yongji Xie <[email-masked]>
Date: Fri, 29 Jan 2016 18:40:02 +0800

On 2016/1/29 6:46, Alex Williamson wrote:
> On Fri, 2016-01-15 at 15:06 +0800, Yongji Xie wrote:
>> MSI-X tables are not allowed to be mmapped in vfio-pci
>> driver in case that user get to touch this directly.
>> This will cause some performance issues when when PCI
>> adapters have critical registers in the same page as
>> the MSI-X table.
>>   
>> However, some kind of PCI host bridge such as IODA bridge
>> on Power support filtering of MSIs, which can ensure that a
>> given pci device can only shoot the MSIs assigned for it.
>> So we think it's safe to expose the MSI-X table to userspace
>> if filtering of MSIs is supported because the exposed MSI-X
>> table can't be used to do harm to other memory space.
>>   
>> To support this case, this patch adds a pci_host_bridge
>> attribute to indicate if this PCI host bridge supports
>> filtering of MSIs.
>>   
>> Signed-off-by: Yongji Xie <[email-masked]>
>> ---
>>   drivers/pci/host-bridge.c |    6 ++++++
>>   include/linux/pci.h       |    3 +++
>>   2 files changed, 9 insertions(+)
>>   
>> diff --git a/drivers/pci/host-bridge.c b/drivers/pci/host-bridge.c
>> index 5f4a2e0..c029267 100644
>> --- a/drivers/pci/host-bridge.c
>> +++ b/drivers/pci/host-bridge.c
>> @@ -96,3 +96,9 @@ void pcibios_bus_to_resource(struct pci_bus *bus, struct resource *res,
>>   	res->end = region->end + offset;
>>   }
>>   EXPORT_SYMBOL(pcibios_bus_to_resource);
>> +
>> +bool pci_host_bridge_msi_filtered_enabled(struct pci_dev *pdev)
>> +{
>> +	return pci_find_host_bridge(pdev->bus)->msi_filtered;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_host_bridge_msi_filtered_enabled);
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index b640d65..b952b78 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -412,6 +412,7 @@ struct pci_host_bridge {
>>   	void (*release_fn)(struct pci_host_bridge *);
>>   	void *release_data;
>>   	unsigned int ignore_reset_delay:1;	/* for entire hierarchy */
>> +	unsigned int msi_filtered:1;	/* support filtering of MSIs */
>>   	/* Resource alignment requirements */
>>   	resource_size_t (*align_resource)(struct pci_dev *dev,
>>   			const struct resource *res,
>> @@ -430,6 +431,8 @@ void pci_set_host_bridge_release(struct pci_host_bridge *bridge,
>>   
>>   int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge);
>>   
>> +bool pci_host_bridge_msi_filtered_enabled(struct pci_dev *pdev);
>> +
>>   /*
>>    * The first PCI_BRIDGE_RESOURCE_NUM PCI bus resources (those that correspond
>>    * to P2P or CardBus bridge windows) go in a table.  Additional ones (for
> Don't we already have a flag for this in the IOMMU space?
>
> enum iommu_cap {
>          IOMMU_CAP_CACHE_COHERENCY,      /* IOMMU can enforce cache coherent DMA
>                                             transactions */
> --->    IOMMU_CAP_INTR_REMAP,           /* IOMMU supports interrupt isolation */
>          IOMMU_CAP_NOEXEC,               /* IOMMU_NOEXEC flag */
> };
>

I saw this flag had been enabled in x86 and ARM arch.

I'm not sure whether we can mmap MSI-X table in those archs. I just 
verify it on PPC64 arch.

Regards.
Yongji Xie