Re: [Qemu-ppc] [RFC PATCH v2 02/13] spapr_iommu: Disable in-kernel IOMMU tables for >4GB windows

[David Gibson]

On Fri, Aug 15, 2014 at 08:12:24PM +1000, Alexey Kardashevskiy wrote:
> The existing KVM_CREATE_SPAPR_TCE ioctl only support 4G windows max.
> We are going to add huge DMA windows support so this will create small
> window and unexpectedly fail later.
> 
> This disables KVM_CREATE_SPAPR_TCE for windows bigger that 4GB. Since
> those windows are normally mapped at the boot time, there will be no
> performance impact.
> 
> Signed-off-by: Alexey Kardashevskiy <address@hidden>

I think perhaps the crucial point here is that the window size
parameter to the kernel ioctl() is only 32-bit, so there's no way of
expressing a TCE window > 4GB.

> ---
>  hw/ppc/spapr_iommu.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> index f6e32a4..36f5d27 100644
> --- a/hw/ppc/spapr_iommu.c
> +++ b/hw/ppc/spapr_iommu.c
> @@ -113,11 +113,11 @@ static MemoryRegionIOMMUOps spapr_iommu_ops = {
>  static int spapr_tce_table_realize(DeviceState *dev)
>  {
>      sPAPRTCETable *tcet = SPAPR_TCE_TABLE(dev);
> +    uint64_t window_size = tcet->nb_table << tcet->page_shift;

tcet->nb_table is only 32-bit itself, so this isn't going to work as
intended without a cast.
-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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