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

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(-)

On Thu, 13 Apr 2017 17:05:27 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> 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.

Ping?


> 
> 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;



--
Alexey

On Thu, 2017-04-13 at 07:05:27 UTC, Alexey Kardashevskiy wrote:
> 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>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/e49a6a2173346d316c0e65d054a3cd

cheers