RE: [PATCH v4 13/14] vtd: use a bit field for context_entry

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant <paul@xxxxxxx>
> Sent: Tuesday, August 4, 2020 9:42 PM
> 
> From: Paul Durrant <pdurrant@xxxxxxxxxx>
> 
> This removes the need for much shifting, masking and several magic
> numbers.
> On the whole it makes the code quite a bit more readable.

similarly, I feel the readability is worse such as slptp. We may use bitfeld
to define the structure, but the function name may be kept with current
way...

Thanks
kevin

> 
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> ---
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> v4:
>  - New in v4
> ---
>  xen/drivers/passthrough/vtd/iommu.c   |  8 ++--
>  xen/drivers/passthrough/vtd/iommu.h   | 65 +++++++++++++++++----------
>  xen/drivers/passthrough/vtd/utils.c   |  6 +--
>  xen/drivers/passthrough/vtd/x86/ats.c |  2 +-
>  4 files changed, 49 insertions(+), 32 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/vtd/iommu.c
> b/xen/drivers/passthrough/vtd/iommu.c
> index 76025f6ccd..766d33058e 100644
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -86,8 +86,6 @@ static int domain_iommu_domid(struct domain *d,
>      return -1;
>  }
> 
> -#define DID_FIELD_WIDTH 16
> -#define DID_HIGH_OFFSET 8
>  static int context_set_domain_id(struct context_entry *context,
>                                   struct domain *d,
>                                   struct vtd_iommu *iommu)
> @@ -121,7 +119,7 @@ static int context_set_domain_id(struct
> context_entry *context,
>      }
> 
>      set_bit(i, iommu->domid_bitmap);
> -    context->hi |= (i & ((1 << DID_FIELD_WIDTH) - 1)) << DID_HIGH_OFFSET;
> +    context_set_did(*context, i);
>      return 0;
>  }
> 
> @@ -135,7 +133,7 @@ static int context_get_domain_id(struct
> context_entry *context,
>      {
>          nr_dom = cap_ndoms(iommu->cap);
> 
> -        dom_index = context_domain_id(*context);
> +        dom_index = context_did(*context);
> 
>          if ( dom_index < nr_dom && iommu->domid_map )
>              domid = iommu->domid_map[dom_index];
> @@ -1396,7 +1394,7 @@ int domain_context_mapping_one(
>              return -ENOMEM;
>          }
> 
> -        context_set_address_root(*context, pgd_maddr);
> +        context_set_slptp(*context, pgd_maddr);
>          if ( ats_enabled && ecap_dev_iotlb(iommu->ecap) )
>              context_set_translation_type(*context, CONTEXT_TT_DEV_IOTLB);
>          else
> diff --git a/xen/drivers/passthrough/vtd/iommu.h
> b/xen/drivers/passthrough/vtd/iommu.h
> index 031ac5f66c..509d13918a 100644
> --- a/xen/drivers/passthrough/vtd/iommu.h
> +++ b/xen/drivers/passthrough/vtd/iommu.h
> @@ -199,6 +199,7 @@ struct root_entry {
>          };
>      };
>  };
> +#define ROOT_ENTRY_NR (PAGE_SIZE_4K / sizeof(struct root_entry))
> 
>  #define root_present(r) (r).p
>  #define set_root_present(r) do { (r).p = 1; } while (0)
> @@ -208,35 +209,53 @@ struct root_entry {
>      do { (r).ctp = ((val) >> PAGE_SHIFT_4K); } while (0)
> 
>  struct context_entry {
> -    u64 lo;
> -    u64 hi;
> +    union {
> +        __uint128_t val;
> +        struct { uint64_t lo, hi; };
> +        struct {
> +            /* 0 - 63 */
> +            uint64_t p:1;
> +            uint64_t fpd:1;
> +            uint64_t tt:2;
> +            uint64_t reserved0:8;
> +            uint64_t slptp:52;
> +
> +            /* 64 - 127 */
> +            uint64_t aw:3;
> +            uint64_t ignored:4;
> +            uint64_t reserved1:1;
> +            uint64_t did:16;
> +            uint64_t reserved2:40;
> +        };
> +    };
>  };
> -#define ROOT_ENTRY_NR (PAGE_SIZE_4K/sizeof(struct root_entry))
> -#define context_present(c) ((c).lo & 1)
> -#define context_fault_disable(c) (((c).lo >> 1) & 1)
> -#define context_translation_type(c) (((c).lo >> 2) & 3)
> -#define context_address_root(c) ((c).lo & PAGE_MASK_4K)
> -#define context_address_width(c) ((c).hi &  7)
> -#define context_domain_id(c) (((c).hi >> 8) & ((1 << 16) - 1))
> -
> -#define context_set_present(c) do {(c).lo |= 1;} while(0)
> -#define context_clear_present(c) do {(c).lo &= ~1;} while(0)
> -#define context_set_fault_enable(c) \
> -    do {(c).lo &= (((u64)-1) << 2) | 1;} while(0)
> -
> -#define context_set_translation_type(c, val) do { \
> -        (c).lo &= (((u64)-1) << 4) | 3; \
> -        (c).lo |= (val & 3) << 2; \
> -    } while(0)
> +
> +#define context_present(c) (c).p
> +#define context_set_present(c) do { (c).p = 1; } while (0)
> +#define context_clear_present(c) do { (c).p = 0; } while (0)
> +
> +#define context_fault_disable(c) (c).fpd
> +#define context_set_fault_enable(c) do { (c).fpd = 1; } while (0)
> +
> +#define context_translation_type(c) (c).tt
> +#define context_set_translation_type(c, val) do { (c).tt = val; } while (0)
>  #define CONTEXT_TT_MULTI_LEVEL 0
>  #define CONTEXT_TT_DEV_IOTLB   1
>  #define CONTEXT_TT_PASS_THRU   2
> 
> -#define context_set_address_root(c, val) \
> -    do {(c).lo &= 0xfff; (c).lo |= (val) & PAGE_MASK_4K ;} while(0)
> +#define context_slptp(c) ((c).slptp << PAGE_SHIFT_4K)
> +#define context_set_slptp(c, val) \
> +    do { (c).slptp = (val) >> PAGE_SHIFT_4K; } while (0)
> +
> +#define context_address_width(c) (c).aw
>  #define context_set_address_width(c, val) \
> -    do {(c).hi &= 0xfffffff8; (c).hi |= (val) & 7;} while(0)
> -#define context_clear_entry(c) do {(c).lo = 0; (c).hi = 0;} while(0)
> +    do { (c).aw = (val); } while (0)
> +
> +#define context_did(c) (c).did
> +#define context_set_did(c, val) \
> +    do { (c).did = (val); } while (0)
> +
> +#define context_clear_entry(c) do { (c).val = 0; } while (0)
> 
>  /* page table handling */
>  #define LEVEL_STRIDE       (9)
> diff --git a/xen/drivers/passthrough/vtd/utils.c
> b/xen/drivers/passthrough/vtd/utils.c
> index 4c85242894..eae0c43269 100644
> --- a/xen/drivers/passthrough/vtd/utils.c
> +++ b/xen/drivers/passthrough/vtd/utils.c
> @@ -129,9 +129,8 @@ void print_vtd_entries(struct vtd_iommu *iommu, int
> bus, int devfn, u64 gmfn)
>          return;
>      }
> 
> -    val = ctxt_entry[devfn].lo;
> -    printk("    context[%02x] = %"PRIx64"_%"PRIx64"\n",
> -           devfn, ctxt_entry[devfn].hi, val);
> +    printk("    context[%02x] = %"PRIx64"_%"PRIx64"\n", devfn,
> +           ctxt_entry[devfn].hi, ctxt_entry[devfn].lo);
>      if ( !context_present(ctxt_entry[devfn]) )
>      {
>          unmap_vtd_domain_page(ctxt_entry);
> @@ -140,6 +139,7 @@ void print_vtd_entries(struct vtd_iommu *iommu, int
> bus, int devfn, u64 gmfn)
>      }
> 
>      level = agaw_to_level(context_address_width(ctxt_entry[devfn]));
> +    val = context_slptp(ctxt_entry[devfn]);
>      unmap_vtd_domain_page(ctxt_entry);
>      if ( level != VTD_PAGE_TABLE_LEVEL_3 &&
>           level != VTD_PAGE_TABLE_LEVEL_4)
> diff --git a/xen/drivers/passthrough/vtd/x86/ats.c
> b/xen/drivers/passthrough/vtd/x86/ats.c
> index 8369415dcc..a7bbd3198a 100644
> --- a/xen/drivers/passthrough/vtd/x86/ats.c
> +++ b/xen/drivers/passthrough/vtd/x86/ats.c
> @@ -92,7 +92,7 @@ static bool device_in_domain(const struct vtd_iommu
> *iommu,
> 
>      context_entries = map_vtd_domain_page(root_ctp(*root_entry));
>      context_entry = &context_entries[pdev->devfn];
> -    if ( context_domain_id(*context_entry) != did )
> +    if ( context_did(*context_entry) != did )
>          goto out;
> 
>      tt = context_translation_type(*context_entry);
> --
> 2.20.1