linux-kernel - [ 043/135] xen: Use correct masking in xen_swiotlb_alloc

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Message-Id: <20120917003632.215097822@decadent.org.uk>
Date:	Mon, 17 Sep 2012 01:37:08 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Ronny Hegewald <ronny.hegewald@...ine.de>,
	Stefano Panella <stefano.panella@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [ 043/135] xen: Use correct masking in xen_swiotlb_alloc_coherent.

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ronny Hegewald <ronny.hegewald@...ine.de>

commit b5031ed1be0aa419250557123633453753181643 upstream.

When running 32-bit pvops-dom0 and a driver tries to allocate a coherent
DMA-memory the xen swiotlb-implementation returned memory beyond 4GB.

The underlaying reason is that if the supplied driver passes in a
DMA_BIT_MASK(64) ( hwdev->coherent_dma_mask is set to 0xffffffffffffffff)
our dma_mask will be u64 set to 0xffffffffffffffff even if we set it to
DMA_BIT_MASK(32) previously. Meaning we do not reset the upper bits.
By using the dma_alloc_coherent_mask function - it does the proper casting
and we get 0xfffffffff.

This caused not working sound on a system with 4 GB and a 64-bit
compatible sound-card with sets the DMA-mask to 64bit.

On bare-metal and the forward-ported xen-dom0 patches from OpenSuse a coherent
DMA-memory is always allocated inside the 32-bit address-range by calling
dma_alloc_coherent_mask.

This patch adds the same functionality to xen swiotlb and is a rebase of the
original patch from Ronny Hegewald which never got upstream b/c the
underlaying reason was not understood until now.

The original email with the original patch is in:
http://old-list-archives.xen.org/archives/html/xen-devel/2010-02/msg00038.html
the original thread from where the discussion started is in:
http://old-list-archives.xen.org/archives/html/xen-devel/2010-01/msg00928.html

Signed-off-by: Ronny Hegewald <ronny.hegewald@...ine.de>
Signed-off-by: Stefano Panella <stefano.panella@...rix.com>
Acked-By: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/xen/swiotlb-xen.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 1afb4fb..4d51948 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -232,7 +232,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 		return ret;

 	if (hwdev && hwdev->coherent_dma_mask)
-		dma_mask = hwdev->coherent_dma_mask;
+		dma_mask = dma_alloc_coherent_mask(hwdev, flags);

 	phys = virt_to_phys(ret);
 	dev_addr = xen_phys_to_bus(phys);

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