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Date:   Tue, 24 Jan 2017 14:52:08 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Robin Murphy <robin.murphy@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>, mark.rutland@....com,
        will.deacon@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linuxarm@...wei.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        john.garry@...wei.com, guohanjun@...wei.com
Subject: Re: [RFC 2/4] irqchip, gicv3-its:Workaround for HiSilicon erratum
 161010801

On 24/01/17 14:41, Robin Murphy wrote:
> 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@...wei.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.

We're in violent agreement, and I'll leave the matter into your capable
hands! ;-)

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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