Re: [PATCH] xen: Add __GFP_DMA flag when xen_swiotlb_init gets free pages.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Apr 20, 2015 at 06:48:24PM +0800, Chen Baozi wrote:
> Make sure that xen_swiotlb_init allocates buffers that is DMA capable.
> 
> Signed-off-by: Chen Baozi <baozich@gmail.com>
> ---
>  drivers/xen/swiotlb-xen.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 810ad41..7345afd 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -235,7 +235,8 @@ retry:
>  #define SLABS_PER_PAGE (1 << (PAGE_SHIFT - IO_TLB_SHIFT))
>  #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
>  		while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
> -			xen_io_tlb_start = (void *)__get_free_pages(__GFP_NOWARN, order);
> +			xen_io_tlb_start = (void *)__get_free_pages(
> +						__GFP_NOWARN|__GFP_DMA, order);

This is not good for x86 PV guests - as the GFP_DMA pool does not really
have pages below 4GB.

Could you  make this __GFP_DMA be dependent on (!xen_pv_domain()) or such?

>  			if (xen_io_tlb_start)
>  				break;
>  			order--;
> -- 
> 2.1.4
> 
> 
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