[RFC PATCH kernel] powerpc/ioda: Set "read" permission when "write" is set

Alexey Kardashevskiy aik at ozlabs.ru
Tue Jan 19 14:52:19 AEDT 2016


On 01/13/2016 01:24 PM, Douglas Miller wrote:
>
>
> On 01/12/2016 05:07 PM, Benjamin Herrenschmidt wrote:
>> On Tue, 2016-01-12 at 15:40 +1100, Alexey Kardashevskiy wrote:
>>> Quite often drivers set only "write" permission assuming that this
>>> includes "read" permission as well and this works on plenty
>>> platforms.
>>> However IODA2 is strict about this and produces an EEH when "read"
>>> permission is not and reading happens.
>>>
>>> This adds a workaround in IODA code to always add the "read" bit when
>>> the "write" bit is set.
>>>
>>> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>>> ---
>>>
>>>
>>> Ben, what was the driver which did not set "read" and caused EEH?
>> aacraid
>>
>> Cheers,
>> Ben.
> Just to be precise, the driver wasn't responsible for setting READ. The
> driver called scsi_dma_map() and the scsicmd was set (by scsi layer) as
> DMA_FROM_DEVICE so the current code would set the permissions to
> WRITE-ONLY. Previously, and in other architectures, this scsicmd would have
> resulted in READ+WRITE permissions on the DMA map.


Does the patch fix the issue? Thanks.



>>
>>> ---
>>>   arch/powerpc/platforms/powernv/pci.c | 6 ++++++
>>>   1 file changed, 6 insertions(+)
>>>
>>> diff --git a/arch/powerpc/platforms/powernv/pci.c
>>> b/arch/powerpc/platforms/powernv/pci.c
>>> index f2dd772..c7dcae5 100644
>>> --- a/arch/powerpc/platforms/powernv/pci.c
>>> +++ b/arch/powerpc/platforms/powernv/pci.c
>>> @@ -601,6 +601,9 @@ int pnv_tce_build(struct iommu_table *tbl, long
>>> index, long npages,
>>>       u64 rpn = __pa(uaddr) >> tbl->it_page_shift;
>>>       long i;
>>> +    if (proto_tce & TCE_PCI_WRITE)
>>> +        proto_tce |= TCE_PCI_READ;
>>> +
>>>       for (i = 0; i < npages; i++) {
>>>           unsigned long newtce = proto_tce |
>>>               ((rpn + i) << tbl->it_page_shift);
>>> @@ -622,6 +625,9 @@ int pnv_tce_xchg(struct iommu_table *tbl, long
>>> index,
>>>       BUG_ON(*hpa & ~IOMMU_PAGE_MASK(tbl));
>>> +    if (newtce & TCE_PCI_WRITE)
>>> +        newtce |= TCE_PCI_READ;
>>> +
>>>       oldtce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
>>>       *hpa = be64_to_cpu(oldtce) & ~(TCE_PCI_READ |
>>> TCE_PCI_WRITE);
>>>       *direction = iommu_tce_direction(oldtce);
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>
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-- 
Alexey


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