Re: [Qemu-ppc] [PATCH qemu v2] vfio/spapr: Allow backing bigger guest IOMMU pages with smaller physical pages

[David Gibson]

On Wed, Jun 20, 2018 at 07:10:12PM +1000, Alexey Kardashevskiy wrote:
> At the moment the PPC64/pseries guest only supports 4K/64K/16M IOMMU
> pages and POWER8 CPU supports the exact same set of page size so
> so far things worked fine.
> 
> However POWER9 supports different set of sizes - 4K/64K/2M/1G and
> the last two - 2M and 1G - are not even allowed in the paravirt interface
> (RTAS DDW) so we always end up using 64K IOMMU pages, although we could
> back guest's 16MB IOMMU pages with 2MB pages on the host.
> 
> This stores the supported host IOMMU page sizes in VFIOContainer and uses
> this later when creating a new DMA window. This uses the system page size
> (64k normally, 2M/16M/1G if hugepages used) as the upper limit of
> the IOMMU pagesize.
> 
> This changes the type of @pagesize to uint64_t as this is what
> memory_region_iommu_get_min_page_size() returns and clz64() takes.
> 
> There should be no behavioral changes on platforms other than pseries.
> The guest will keep using the IOMMU page size selected by the PHB pagesize
> property as this only changes the underlying hardware TCE table
> granularity.
> 
> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> ---
> Changes:
> v2:
> * fixed biggest but smaller page size calculation
> * limit IOMMU pagesize to the system pagesize

Sorry, this fell of my radar for a bit.

I've now applied it to ppc-for-3.1.

> ---
>  include/hw/vfio/vfio-common.h |  1 +
>  hw/vfio/common.c              |  3 +++
>  hw/vfio/spapr.c               | 21 ++++++++++++++++++++-
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index a903692..c20524d 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -73,6 +73,7 @@ typedef struct VFIOContainer {
>      unsigned iommu_type;
>      int error;
>      bool initialized;
> +    unsigned long pgsizes;
>      /*
>       * This assumes the host IOMMU can support only a single
>       * contiguous IOVA window.  We may need to generalize that in
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index fb396cf..40f0356 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -1108,6 +1108,7 @@ static int vfio_connect_container(VFIOGroup *group, 
> AddressSpace *as,
>              info.iova_pgsizes = 4096;
>          }
>          vfio_host_win_add(container, 0, (hwaddr)-1, info.iova_pgsizes);
> +        container->pgsizes = info.iova_pgsizes;
>      } else if (ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU) ||
>                 ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_v2_IOMMU)) {
>          struct vfio_iommu_spapr_tce_info info;
> @@ -1172,6 +1173,7 @@ static int vfio_connect_container(VFIOGroup *group, 
> AddressSpace *as,
>          }
>  
>          if (v2) {
> +            container->pgsizes = info.ddw.pgsizes;
>              /*
>               * There is a default window in just created container.
>               * To make region_add/del simpler, we better remove this
> @@ -1186,6 +1188,7 @@ static int vfio_connect_container(VFIOGroup *group, 
> AddressSpace *as,
>              }
>          } else {
>              /* The default table uses 4K pages */
> +            container->pgsizes = 0x1000;
>              vfio_host_win_add(container, info.dma32_window_start,
>                                info.dma32_window_start +
>                                info.dma32_window_size - 1,
> diff --git a/hw/vfio/spapr.c b/hw/vfio/spapr.c
> index 259397c..becf71a 100644
> --- a/hw/vfio/spapr.c
> +++ b/hw/vfio/spapr.c
> @@ -15,6 +15,7 @@
>  
>  #include "hw/vfio/vfio-common.h"
>  #include "hw/hw.h"
> +#include "exec/ram_addr.h"
>  #include "qemu/error-report.h"
>  #include "trace.h"
>  
> @@ -144,9 +145,27 @@ int vfio_spapr_create_window(VFIOContainer *container,
>  {
>      int ret;
>      IOMMUMemoryRegion *iommu_mr = IOMMU_MEMORY_REGION(section->mr);
> -    unsigned pagesize = memory_region_iommu_get_min_page_size(iommu_mr);
> +    uint64_t pagesize = memory_region_iommu_get_min_page_size(iommu_mr);
>      unsigned entries, pages;
>      struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create) };
> +    long systempagesize = qemu_getrampagesize();
> +
> +    /*
> +     * The host might not support the guest supported IOMMU page size,
> +     * so we will use smaller physical IOMMU pages to back them.
> +     */
> +    if (pagesize > systempagesize) {
> +        pagesize = systempagesize;
> +    }
> +    pagesize = 1ULL << (63 - clz64(container->pgsizes &
> +                                   (pagesize | (pagesize - 1))));
> +    if (!pagesize) {
> +        error_report("Host doesn't support page size 0x%"PRIx64
> +                     ", the supported mask is 0x%lx",
> +                     memory_region_iommu_get_min_page_size(iommu_mr),
> +                     container->pgsizes);
> +        return -EINVAL;
> +    }
>  
>      /*
>       * FIXME: For VFIO iommu types which have KVM acceleration to

-- 
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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