[PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

[PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

[Leonardo Bras]

As of today, if the DDW is big enough to fit (1 << MAX_PHYSMEM_BITS) it's
possible to use direct DMA mapping even with pmem region.

But, if that happens, the window size (len) is set to
(MAX_PHYSMEM_BITS - page_shift) instead of MAX_PHYSMEM_BITS, causing a
pagesize times smaller DDW to be created, being insufficient for correct
usage.

Fix this so the correct window size is used in this case.

Fixes: bf6e2d562bbc4("powerpc/dma: Fallback to dma_ops when persistent memory present")
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 9fc5217f0c8e..836cbbe0ecc5 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1229,7 +1229,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	if (pmem_present) {
 		if (query.largest_available_block >=
 		    (1ULL << (MAX_PHYSMEM_BITS - page_shift)))
-			len = MAX_PHYSMEM_BITS - page_shift;
+			len = MAX_PHYSMEM_BITS;
 		else
 			dev_info(&dev->dev, "Skipping ibm,pmemory");
 	}
-- 
2.30.2

Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

[Alexey Kardashevskiy]

On 20/04/2021 14:54, Leonardo Bras wrote:
> As of today, if the DDW is big enough to fit (1 << MAX_PHYSMEM_BITS) it's
> possible to use direct DMA mapping even with pmem region.
> 
> But, if that happens, the window size (len) is set to
> (MAX_PHYSMEM_BITS - page_shift) instead of MAX_PHYSMEM_BITS, causing a
> pagesize times smaller DDW to be created, being insufficient for correct
> usage.
> 
> Fix this so the correct window size is used in this case.

Good find indeed.

afaict this does not create a huge problem though as 
query.largest_available_block is always smaller than (MAX_PHYSMEM_BITS - 
page_shift) where it matters (phyp).


Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>


> Fixes: bf6e2d562bbc4("powerpc/dma: Fallback to dma_ops when persistent memory present")
> Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
> ---
>   arch/powerpc/platforms/pseries/iommu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 9fc5217f0c8e..836cbbe0ecc5 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -1229,7 +1229,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>   	if (pmem_present) {
>   		if (query.largest_available_block >=
>   		    (1ULL << (MAX_PHYSMEM_BITS - page_shift)))
> -			len = MAX_PHYSMEM_BITS - page_shift;
> +			len = MAX_PHYSMEM_BITS;
>   		else
>   			dev_info(&dev->dev, "Skipping ibm,pmemory");
>   	}
> 

-- 
Alexey

Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

[Leonardo Bras]

On Tue, 2021-04-20 at 15:18 +1000, Alexey Kardashevskiy wrote:
> 
> On 20/04/2021 14:54, Leonardo Bras wrote:
> > As of today, if the DDW is big enough to fit (1 << MAX_PHYSMEM_BITS) it's
> > possible to use direct DMA mapping even with pmem region.
> > 
> > But, if that happens, the window size (len) is set to
> > (MAX_PHYSMEM_BITS - page_shift) instead of MAX_PHYSMEM_BITS, causing a
> > pagesize times smaller DDW to be created, being insufficient for correct
> > usage.
> > 
> > Fix this so the correct window size is used in this case.
> 
> Good find indeed.
> 
> afaict this does not create a huge problem though as 
> query.largest_available_block is always smaller than (MAX_PHYSMEM_BITS - 
> page_shift) where it matters (phyp).
> 
> 
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 

Thanks for reviewing!

Leonardo Bras

Re: [PATCH 1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem

[Michael Ellerman]

On Tue, 20 Apr 2021 01:54:04 -0300, Leonardo Bras wrote:
> As of today, if the DDW is big enough to fit (1 << MAX_PHYSMEM_BITS) it's
> possible to use direct DMA mapping even with pmem region.
> 
> But, if that happens, the window size (len) is set to
> (MAX_PHYSMEM_BITS - page_shift) instead of MAX_PHYSMEM_BITS, causing a
> pagesize times smaller DDW to be created, being insufficient for correct
> usage.
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/pseries/iommu: Fix window size for direct mapping with pmem
      https://git.kernel.org/powerpc/c/a9d2f9bb225fd2a764aef57738ab6c7f38d782ae

cheers