Patch "powerpc/powernv/ioda2: Gracefully fail if too many TCE levels requested" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/powernv/ioda2: Gracefully fail if too many TCE levels requested

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-powernv-ioda2-gracefully-fail-if-too-many-tce-levels-requested.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexey Kardashevskiy <[email protected]>
Date: Wed, 22 Feb 2017 15:43:59 +1100
Subject: powerpc/powernv/ioda2: Gracefully fail if too many TCE levels requested

From: Alexey Kardashevskiy <[email protected]>

[ Upstream commit 7aafac11e308d37ed3c509829bb43d80c1811ac3 ]

The IODA2 specification says that a 64 DMA address cannot use top 4 bits (3 are reserved and one is a "TVE select"); bottom page_shift bits cannot be used for multilevel table addressing either.

The existing IODA2 table allocation code aligns the minimum TCE table size to PAGE_SIZE so in the case of 64K system pages and 4K IOMMU pages, we have 64-4-12=48 bits. Since 64K page stores 8192 TCEs, i.e. needs 13 bits, the maximum number of levels is 48/13 = 3 so we physically cannot address more and EEH happens on DMA accesses.

This adds a check that too many levels were requested.

It is still possible to have 5 levels in the case of 4K system page size.

---
 arch/powerpc/platforms/powernv/pci-ioda.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -2270,6 +2270,9 @@ static long pnv_pci_ioda2_table_alloc_pa
 	level_shift = entries_shift + 3;
 	level_shift = max_t(unsigned, level_shift, PAGE_SHIFT);
 
+	if ((level_shift - 3) * levels + page_shift >= 60)
+		return -EINVAL;
+
 	/* Allocate TCE table */
 	addr = pnv_pci_ioda2_table_do_alloc_pages(nid, level_shift,
 			levels, tce_table_size, &offset, &total_allocated);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/powerpc-powernv-ioda2-gracefully-fail-if-too-many-tce-levels-requested.patch