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

On 01/12/2016 05:07 PM, Benjamin Herrenschmidt wrote:

On Tue, 2016-01-12 at 15:40 +1100, Alexey Kardashevskiy wrote:

quoted

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@kernel.crashing.org>
Signed-off-by: Alexey Kardashevskiy <redacted>
---


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.

quoted

---
  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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