On Tue, 31 Jul 2012, Konrad Rzeszutek Wilk wrote:
> 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.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> ---
> arch/x86/xen/pci-swiotlb-xen.c | 12 ++++++++++++
> 1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
> index b6a5340..0d5a214 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 +54,13 @@ 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 native SWIOTLB if no_iommu == 0
> + * (so no iommu=X command line over-writes). So disable the native
> + * SWIOTLB. */
Maybe rewording it would be a good idea:
/* pci_swiotlb_detect_4gb turns on native SWIOTLB if no_iommu == 0
* (so no iommu=X command line over-writes).
* Considering that PV guests don't normally have PCI devices it is not
* useful to us so we set no_iommu to 1 here */
> + if (max_pfn > MAX_DMA32_PFN)
> + no_iommu = 1;
> +#endif
> return xen_swiotlb;
> }
>
> --
> 1.7.7.6
>
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