[PATCH kernel] powerpc/powernv: Fix iommu table size calculation hook for small tables

[Alexey Kardashevskiy <aik@ozlabs.ru>]

When the userspace requests a small TCE table (which takes less than
the system page size) and more than 1 TCE level, the existing code
returns a single page size which is a bug as each additional TCE level
requires at least one page and this is what
pnv_pci_ioda2_table_alloc_pages() does. And we end up seeing
WARN_ON(!ret && ((*ptbl)->it_allocated_size != table_size))
in drivers/vfio/vfio_iommu_spapr_tce.c.

This replaces incorrect _ALIGN_UP() (which aligns zero up to zero) with
max_t() to fix the bug.

Besides removing WARN_ON(), there should be no other changes in
behaviour.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 arch/powerpc/platforms/powernv/pci-ioda.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index 6d0da5dfc955..a0d046adcf45 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -2538,7 +2538,8 @@ static unsigned long pnv_pci_ioda2_get_table_size(__u32 page_shift,
 
 		tce_table_size /= direct_table_size;
 		tce_table_size <<= 3;
-		tce_table_size = _ALIGN_UP(tce_table_size, direct_table_size);
+		tce_table_size = max_t(unsigned long,
+				tce_table_size, direct_table_size);
 	}
 
 	return bytes;
-- 
2.11.0