On Tue, 31 Jul 2012, Konrad Rzeszutek Wilk wrote:
> commit 21ef55f4ab2b6d63eb0ed86abbc959d31377853b
> Author: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Date: Fri Jul 27 20:16:00 2012 -0400
>
> xen/swiotlb: With more than 4GB on 64-bit, disable the native SWIOTLB.
>
> If a PV guest is booted the native SWIOTLB should not be
> turned on. It does not help us (we don't have any PCI devices)
> and it eats 64MB of good memory. In the case of PV guests
> with PCI devices we need the Xen-SWIOTLB one.
>
> [v1: Rewrite comment per Stefano's suggestion]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
Acked-by: Stefano Stabellini <stefano.stabell...@eu.citrix.com>
> diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
> index b6a5340..1c17227 100644
> --- a/arch/x86/xen/pci-swiotlb-xen.c
> +++ b/arch/x86/xen/pci-swiotlb-xen.c
> @@ -8,6 +8,11 @@
> #include <xen/xen.h>
> #include <asm/iommu_table.h>
>
> +#ifdef CONFIG_X86_64
> +#include <asm/iommu.h>
> +#include <asm/dma.h>
> +#endif
> +
> int xen_swiotlb __read_mostly;
>
> static struct dma_map_ops xen_swiotlb_dma_ops = {
> @@ -49,6 +54,15 @@ int __init pci_xen_swiotlb_detect(void)
> * the 'swiotlb' flag is the only one turning it on. */
> swiotlb = 0;
>
> +#ifdef CONFIG_X86_64
> + /* pci_swiotlb_detect_4gb turns on native SWIOTLB if no_iommu == 0
> + * (so no iommu=X command line over-writes).
> + * Considering that PV guests do not want the *native SWIOTLB* but
> + * only Xen SWIOTLB it is not useful to us so set no_iommu=1 here.
> + */
> + if (max_pfn > MAX_DMA32_PFN)
> + no_iommu = 1;
> +#endif
> return xen_swiotlb;
> }
>
>
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