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

[Marc Zyngier <marc.zyngier@arm.com>]

On 24/01/17 15:39, Shameerali Kolothum Thodi wrote:
> +Eric
> 
>> -----Original Message-----
>> From: Robin Murphy [mailto:robin.murphy@arm.com]
>> Sent: Tuesday, January 24, 2017 2:42 PM
>> To: Marc Zyngier; Shameerali Kolothum Thodi; mark.rutland@arm.com;
>> will.deacon@arm.com
>> Cc: linux-arm-kernel@lists.infradead.org; Linuxarm; linux-
>> kernel@vger.kernel.org; devicetree@vger.kernel.org; John Garry;
>> Guohanjun (Hanjun Guo)
>> Subject: Re: [RFC 2/4] irqchip, gicv3-its:Workaround for HiSilicon
>> erratum 161010801
>>
>> 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.
> 
> Is this something that can incorporated in Eric's latest patch series[1]?
> It does mentions reserved regions can be:
> - directly mapped regions
> - regions that cannot be iommu mapped (PCI host bridge windows, ...)
> - MSI regions (because they belong to another address space or because
>   they are not translated by the IOMMU and need special handling)
> 
> Though I am not clear our case comes under "the MSI regions that are
> not translated by the IOMMU and need special handling" or not.

Well, given that in your case, the IOMMU never sees the MSI write, it
definitely falls into the "not translated" category.

As for handling it on top of Eric's series, that's probably the most
reasonable thing to do, which also means that none of this should appear
in the ITS driver. Robin seems to have an idea on how to approach this.

Thanks,

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