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* Re: [Qemu-devel] [PATCH qemu v2] vfio/spapr: Allow backing bigger guest IOMMU pages with smaller physical pages
From: Alexey Kardashevskiy @ 2018-07-24  3:56 UTC (permalink / raw)
  To: David Gibson; +Cc: qemu-devel, qemu-ppc, Alex Williamson
In-Reply-To: <20180723031142.GA6830@umbus.fritz.box>

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On 23/07/2018 13:11, David Gibson wrote:
> 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 <aik@ozlabs.ru>
>> ---
>> 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.


Alex might object that as it does not have his "rb" ;)


> 
>> ---
>>  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
> 

-- 
Alexey


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