Re: [RFC 2/4] irqchip, gicv3-its:Workaround for HiSilicon erratum 161010801

[Robin Murphy <robin.murphy@arm.com>]

On 24/01/17 14:11, Marc Zyngier wrote:
> + Robin,
> 
> On 24/01/17 13:47, Shameerali Kolothum Thodi wrote:
>> The HiSilicon erratum 161010801 describes the limitation of certain
>> HiSilicon platforms to support the SMMU mappings for MSI transactions.
>>
>> On these platforms GICv3 ITS translator is presented with the deviceID
>> by extending the MSI payload data to 64 bits to include the deviceID.
>> Hence, the PCIe controller on this platforms has to differentiate the
>> MSI payload against other DMA payload and has to modify the MSI payload.
>> This basically makes it difficult for this platforms to have a SMMU
>> translation for MSI. Also these platforms doesn't have a proper IIDR
>> register to use the existing IIDR based quirk mechanism.
>>
>> This workaround based on the devicetree binding property, supports
>> bypassing the SMMU for the MSI transactions on this platforms.
>>
>> Signed-off-by: shameer <shameerali.kolothum.thodi@huawei.com>
>> ---
>>  arch/arm64/Kconfig               | 15 ++++++++++++
>>  drivers/irqchip/irq-gic-common.h |  1 +
>>  drivers/irqchip/irq-gic-v3-its.c | 52 +++++++++++++++++++++++++++++++++++++++-
>>  3 files changed, 67 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 0ae0427..8d600b0 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -485,6 +485,21 @@ config CAVIUM_ERRATUM_27456
>>
>>  	  If unsure, say Y.
>>
>> +config HISILICON_ERRATUM_161010801
>> +	bool "HiSilicon erratum 161010801"
>> +	default y
>> +	help
>> +	  Enable workaround for erratum 161010801.
>> +
>> +	  This implements a gicv3-its errata workaround for HiSilicon
>> +	  platforms Hip05/Hip07. These platforms cannot support the MSI
>> +	  interrupt remapping and MSI transaction has to be bypassed by SMMU.
>> +
>> +	  The fix is to avoid calling the remapping hook into the SMMU
>> +	  driver from the its_irq_compose_msi_msg().
>> +
>> +	  If unsure, say Y.
>> +
>>  endmenu
>>
>>
>> diff --git a/drivers/irqchip/irq-gic-common.h b/drivers/irqchip/irq-gic-common.h
>> index 205e5fd..de0385a 100644
>> --- a/drivers/irqchip/irq-gic-common.h
>> +++ b/drivers/irqchip/irq-gic-common.h
>> @@ -26,6 +26,7 @@ struct gic_quirk {
>>  	void (*init)(void *data);
>>  	u32 iidr;
>>  	u32 mask;
>> +	const char *erratum;
>>  };
>>
>>  int gic_configure_irq(unsigned int irq, unsigned int type,
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index f471939..0a326f6 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -44,6 +44,7 @@
>>  #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING		(1ULL << 0)
>>  #define ITS_FLAGS_WORKAROUND_CAVIUM_22375	(1ULL << 1)
>>  #define ITS_FLAGS_WORKAROUND_CAVIUM_23144	(1ULL << 2)
>> +#define ITS_FLAGS_WORKAROUND_HISILICON_161010801	(1ULL << 3)
>>
>>  #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING	(1 << 0)
>>
>> @@ -659,7 +660,8 @@ static void its_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *msg)
>>  	msg->address_hi		= upper_32_bits(addr);
>>  	msg->data		= its_get_event_id(d);
>>
>> -	iommu_dma_map_msi_msg(d->irq, msg);
>> +	if (!(its->flags & ITS_FLAGS_WORKAROUND_HISILICON_161010801))
>> +		iommu_dma_map_msi_msg(d->irq, msg);
> 
> Let's contemplate this for a moment. If we're on the affected ITS, we're
> using the physical address of the GITS_TRANSLATER register. What
> guarantees that this is not going to conflict with an IOVA that DMA is
> going to use? From looking at these patches, my feeling is "not much".
> 
> So if I'm right, you're opening the door to some interesting memory
> corruption if the two regions ever intersect.
>
> Robin, what do you think?

Yup. Unless the ITS physical address is actually reserved from the IOVA
domain, it's still free to be allocated for DMA mappings, and if that
ever happens then you'll get odd bits of data landing in the ITS instead
of RAM, and maybe even locked-up devices or worse if the doorbell gives
back decode errors on read attempts. It's essentially the exact same
problem as we have with memory-mapped PCI windows, and needs to be
solved in the same fashion, i.e. between the SMMU and the IOMMU-DMA code.

Robin.

> 
> 	M.
>