> From: Peter Xu [mailto:pet...@redhat.com]
> Sent: Friday, January 13, 2017 11:06 AM
> 
> From: Aviv Ben-David <bd.a...@gmail.com>
> 
> This capability asks the guest to invalidate cache before each map operation.
> We can use this invalidation to trap map operations in the hypervisor.
> 
> Signed-off-by: Aviv Ben-David <bd.a...@gmail.com>
> Signed-off-by: Peter Xu <pet...@redhat.com>
> ---
>  hw/i386/intel_iommu.c          | 5 +++++
>  hw/i386/intel_iommu_internal.h | 1 +
>  include/hw/i386/intel_iommu.h  | 2 ++
>  3 files changed, 8 insertions(+)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index ec62239..2868e37 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -2107,6 +2107,7 @@ static Property vtd_properties[] = {
>      DEFINE_PROP_ON_OFF_AUTO("eim", IntelIOMMUState, intr_eim,
>                              ON_OFF_AUTO_AUTO),
>      DEFINE_PROP_BOOL("x-buggy-eim", IntelIOMMUState, buggy_eim, false),
> +    DEFINE_PROP_BOOL("cache-mode", IntelIOMMUState, cache_mode_enabled,
> FALSE),
>      DEFINE_PROP_END_OF_LIST(),
>  };
> 
> @@ -2488,6 +2489,10 @@ static void vtd_init(IntelIOMMUState *s)
>          s->ecap |= VTD_ECAP_DT;
>      }
> 
> +    if (s->cache_mode_enabled) {
> +        s->cap |= VTD_CAP_CM;
> +    }
> +

I think some of my old comments are not answered:

1) Better to use caching_mode to follow spec

2) Does it make sense to automatically set this flag if any VFIO device
has been statically assigned when starting Qemu? Also for hot-add
device path, some check of caching mode is required. If not set, 
should we fail hot-add operation? I don't think we have such physical
platform with some devices behind IOMMU while others not.

>      vtd_reset_context_cache(s);
>      vtd_reset_iotlb(s);
> 
> diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
> index 356f188..4104121 100644
> --- a/hw/i386/intel_iommu_internal.h
> +++ b/hw/i386/intel_iommu_internal.h
> @@ -202,6 +202,7 @@
>  #define VTD_CAP_MAMV                (VTD_MAMV << 48)
>  #define VTD_CAP_PSI                 (1ULL << 39)
>  #define VTD_CAP_SLLPS               ((1ULL << 34) | (1ULL << 35))
> +#define VTD_CAP_CM                  (1ULL << 7)
> 
>  /* Supported Adjusted Guest Address Widths */
>  #define VTD_CAP_SAGAW_SHIFT         8
> diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
> index 405c9d1..749eef9 100644
> --- a/include/hw/i386/intel_iommu.h
> +++ b/include/hw/i386/intel_iommu.h
> @@ -257,6 +257,8 @@ struct IntelIOMMUState {
>      uint8_t womask[DMAR_REG_SIZE];  /* WO (write only - read returns 0) */
>      uint32_t version;
> 
> +    bool cache_mode_enabled;        /* RO - is cap CM enabled? */
> +
>      dma_addr_t root;                /* Current root table pointer */
>      bool root_extended;             /* Type of root table (extended or not) 
> */
>      bool dmar_enabled;              /* Set if DMA remapping is enabled */
> --
> 2.7.4


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