linux-kernel - [PATCHv4 0/4]: dma, x86, xen: reduce SWIOTLB usage in Xen guests

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Date:	Thu, 20 Nov 2014 11:50:21 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	<linux-kernel@...r.kernel.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCHv4 0/4]: dma, x86, xen: reduce SWIOTLB usage in Xen guests

On systems where DMA addresses and physical addresses are not 1:1
(such as Xen PV guests), the generic dma_get_required_mask() will not
return the correct mask (since it uses max_pfn).

Some device drivers (such as mptsas, mpt2sas) use
dma_get_required_mask() to set the device's DMA mask to allow them to use
only 32-bit DMA addresses in hardware structures.  This results in
unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits,
impacting performance significantly.

This series allows Xen PV guests to override the default
dma_get_required_mask() with one that calculates the DMA mask from the
maximum MFN (and not the PFN).

Changes in v4:
- Assume 64-bit mask is required.

Changes in v3:
- fix off-by-one in xen_dma_get_required_mask()
- split ia64 changes into separate patch.

Changes in v2:
- split x86 and xen changes into separate patches

David

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