[v2,4/7] memory: provide a MemoryRegion for IOMMUs to log faults

Accesses which do not translate will hit the fault region, which
can then log the access.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 memory.c | 9 ++++++---
 memory.h | 4 ++++
 2 files changed, 10 insertions(+), 3 deletions(-)

On Tue, Oct 30, 2012 at 11:47 AM, Avi Kivity <avi@redhat.com> wrote:
> Accesses which do not translate will hit the fault region, which
> can then log the access.

Maybe special casing the fault region should be avoided, the IOMMU
could set up suitable fault regions by itself.

>
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
>  memory.c | 9 ++++++---
>  memory.h | 4 ++++
>  2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index ba2d4a0..d6b46fd 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -778,7 +778,9 @@ static void memory_region_destructor_rom_device(MemoryRegion *mr)
>  static void memory_region_destructor_iommu(MemoryRegion *mr)
>  {
>      address_space_destroy(mr->iommu_target_as);
> +    address_space_destroy(mr->iommu_fault_as);
>      g_free(mr->iommu_target_as);
> +    g_free(mr->iommu_fault_as);
>  }
>
>  static bool memory_region_wrong_endianness(MemoryRegion *mr)
> @@ -1001,9 +1003,7 @@ static void memory_region_iommu_rw(MemoryRegion *iommu, hwaddr addr,
>              xlat = (tlb.translated_addr & ~tlb.addr_mask) | (addr & tlb.addr_mask);
>              address_space_rw(iommu->iommu_target_as, xlat, buf, clen, is_write);
>          } else {
> -            if (!is_write) {
> -                memset(buf, 0xff, clen);
> -            }
> +            address_space_rw(iommu->iommu_fault_as, addr, buf, clen, is_write);
>          }
>          buf += clen;
>          addr += clen;
> @@ -1068,6 +1068,7 @@ static void memory_region_iommu_write(void *opaque, hwaddr addr,
>  void memory_region_init_iommu(MemoryRegion *mr,
>                                MemoryRegionIOMMUOps *ops,
>                                MemoryRegion *target,
> +                              MemoryRegion *fault,
>                                const char *name,
>                                uint64_t size)
>  {
> @@ -1079,6 +1080,8 @@ void memory_region_init_iommu(MemoryRegion *mr,
>      mr->destructor = memory_region_destructor_iommu;
>      mr->iommu_target_as = g_new(AddressSpace, 1);
>      address_space_init(mr->iommu_target_as, target);
> +    mr->iommu_fault_as = g_new(AddressSpace, 1);
> +    address_space_init(mr->iommu_fault_as, fault);
>  }
>
>  static uint64_t invalid_read(void *opaque, hwaddr addr,
> diff --git a/memory.h b/memory.h
> index 47362c9..6312197 100644
> --- a/memory.h
> +++ b/memory.h
> @@ -162,6 +162,7 @@ struct MemoryRegion {
>      unsigned ioeventfd_nb;
>      MemoryRegionIoeventfd *ioeventfds;
>      struct AddressSpace *iommu_target_as;
> +    struct AddressSpace *iommu_fault_as;
>  };
>
>  struct MemoryRegionPortio {
> @@ -361,12 +362,15 @@ void memory_region_init_reservation(MemoryRegion *mr,
>   * @ops: a function that translates addresses into the @target region
>   * @target: a #MemoryRegion that will be used to satisfy accesses to translated
>   *          addresses
> + * @fault: a #MemoryRegion for servicing failed translations; accessed with
> + *         untranslated addresses
>   * @name: used for debugging; not visible to the user or ABI
>   * @size: size of the region.
>   */
>  void memory_region_init_iommu(MemoryRegion *mr,
>                                MemoryRegionIOMMUOps *ops,
>                                MemoryRegion *target,
> +                              MemoryRegion *fault,
>                                const char *name,
>                                uint64_t size);
>
> --
> 1.7.12
>

On 10/30/2012 09:14 PM, Blue Swirl wrote:
> On Tue, Oct 30, 2012 at 11:47 AM, Avi Kivity <avi@redhat.com> wrote:
>> Accesses which do not translate will hit the fault region, which
>> can then log the access.
> 
> Maybe special casing the fault region should be avoided, the IOMMU
> could set up suitable fault regions by itself.

How can it?  Please elaborate.

I'm not too pleased with using a MemoryRegion for faults, perhaps a
MemoryRegionIOMMUOps::fault() callback would be better.