RE: [PATCH v10 6/7] vtd: use a bit field for context_entry

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

> From: Paul Durrant <paul@xxxxxxx>
> Sent: Friday, November 20, 2020 9:25 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.
> 
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

> ---
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> v10:
>  - Remove macros in favour of direct field access
>  - Adjust field types
>  - Add missing barriers
> 
> v4:
>  - New in v4
> ---
>  xen/drivers/passthrough/vtd/iommu.c   | 36 +++++++++++----------
>  xen/drivers/passthrough/vtd/iommu.h   | 45 +++++++++++++--------------
>  xen/drivers/passthrough/vtd/utils.c   | 10 +++---
>  xen/drivers/passthrough/vtd/x86/ats.c |  6 ++--
>  4 files changed, 47 insertions(+), 50 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/vtd/iommu.c
> b/xen/drivers/passthrough/vtd/iommu.c
> index 1a038541f0a3..fdb472ad6515 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)
> @@ -121,21 +119,22 @@ 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->did = i;
> +
>      return 0;
>  }
> 
>  static int context_get_domain_id(struct context_entry *context,
>                                   struct vtd_iommu *iommu)
>  {
> -    unsigned long dom_index, nr_dom;
>      int domid = -1;
> 
>      if (iommu && context)
>      {
> -        nr_dom = cap_ndoms(iommu->cap);
> +        unsigned long dom_index, nr_dom;
> 
> -        dom_index = context_domain_id(*context);
> +        nr_dom = cap_ndoms(iommu->cap);
> +        dom_index = context->did;
> 
>          if ( dom_index < nr_dom && iommu->domid_map )
>              domid = iommu->domid_map[dom_index];
> @@ -1338,7 +1337,7 @@ int domain_context_mapping_one(
>      context_entries = (struct context_entry *)map_vtd_domain_page(maddr);
>      context = &context_entries[devfn];
> 
> -    if ( context_present(*context) )
> +    if ( context->p )
>      {
>          int res = 0;
> 
> @@ -1382,7 +1381,7 @@ int domain_context_mapping_one(
> 
>      if ( iommu_hwdom_passthrough && is_hardware_domain(domain) )
>      {
> -        context_set_translation_type(*context, CONTEXT_TT_PASS_THRU);
> +        context->tt = CONTEXT_TT_PASS_THRU;
>      }
>      else
>      {
> @@ -1397,11 +1396,11 @@ int domain_context_mapping_one(
>              return -ENOMEM;
>          }
> 
> -        context_set_address_root(*context, pgd_maddr);
> +        context->slptptr = paddr_to_pfn(pgd_maddr);
>          if ( ats_enabled && ecap_dev_iotlb(iommu->ecap) )
> -            context_set_translation_type(*context, CONTEXT_TT_DEV_IOTLB);
> +            context->tt = CONTEXT_TT_DEV_IOTLB;
>          else
> -            context_set_translation_type(*context, CONTEXT_TT_MULTI_LEVEL);
> +            context->tt = CONTEXT_TT_MULTI_LEVEL;
> 
>          spin_unlock(&hd->arch.mapping_lock);
>      }
> @@ -1413,9 +1412,10 @@ int domain_context_mapping_one(
>          return -EFAULT;
>      }
> 
> -    context_set_address_width(*context, level_to_agaw(iommu-
> >nr_pt_levels));
> -    context_set_fault_enable(*context);
> -    context_set_present(*context);
> +    context->aw = level_to_agaw(iommu->nr_pt_levels);
> +    context->fpd = false;
> +    smp_wmb();
> +    context->p = true;
>      iommu_sync_cache(context, sizeof(struct context_entry));
>      spin_unlock(&iommu->lock);
> 
> @@ -1567,17 +1567,19 @@ int domain_context_unmap_one(
>      context_entries = (struct context_entry *)map_vtd_domain_page(maddr);
>      context = &context_entries[devfn];
> 
> -    if ( !context_present(*context) )
> +    if ( !context->p )
>      {
>          spin_unlock(&iommu->lock);
>          unmap_vtd_domain_page(context_entries);
>          return 0;
>      }
> 
> -    context_clear_present(*context);
> -    context_clear_entry(*context);
> +    context->p = false;
> +    smp_wmb();
>      iommu_sync_cache(context, sizeof(struct context_entry));
> 
> +    context->val = 0; /* No need to sync; present bit is already cleared */
> +
>      iommu_domid= domain_iommu_domid(domain, iommu);
>      if ( iommu_domid == -1 )
>      {
> diff --git a/xen/drivers/passthrough/vtd/iommu.h
> b/xen/drivers/passthrough/vtd/iommu.h
> index b14628eec260..33b1abf98526 100644
> --- a/xen/drivers/passthrough/vtd/iommu.h
> +++ b/xen/drivers/passthrough/vtd/iommu.h
> @@ -198,37 +198,34 @@ struct root_entry {
>          };
>      };
>  };
> +#define ROOT_ENTRY_NR (PAGE_SIZE_4K / sizeof(struct root_entry))
> 
>  struct context_entry {
> -    u64 lo;
> -    u64 hi;
> -};
> -#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))
> +    union {
> +        __uint128_t val;
> +        struct { uint64_t lo, hi; };
> +        struct {
> +            /* 0 - 63 */
> +            bool p:1;
> +            bool fpd:1;
> +            uint64_t tt:2;
> 
> -#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_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_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)
> +            unsigned int reserved0:8;
> +            uint64_t slptptr:52;
> +
> +            /* 64 - 127 */
> +            unsigned int aw:3;
> +            unsigned int ignored:4;
> +            unsigned int reserved1:1;
> +            unsigned int did:16;
> +            uint64_t reserved2:40;
> +        };
> +    };
> +};
> 
>  /* page table handling */
>  #define LEVEL_STRIDE       (9)
> diff --git a/xen/drivers/passthrough/vtd/utils.c
> b/xen/drivers/passthrough/vtd/utils.c
> index 5f25a86a535c..4bca160bc663 100644
> --- a/xen/drivers/passthrough/vtd/utils.c
> +++ b/xen/drivers/passthrough/vtd/utils.c
> @@ -129,17 +129,17 @@ 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);
> -    if ( !context_present(ctxt_entry[devfn]) )
> +    printk("    context[%02x] = %"PRIx64"_%"PRIx64"\n", devfn,
> +           ctxt_entry[devfn].hi, ctxt_entry[devfn].lo);
> +    if ( !ctxt_entry[devfn].p )
>      {
>          unmap_vtd_domain_page(ctxt_entry);
>          printk("    ctxt_entry[%02x] not present\n", devfn);
>          return;
>      }
> 
> -    level = agaw_to_level(context_address_width(ctxt_entry[devfn]));
> +    level = agaw_to_level(ctxt_entry[devfn].aw);
> +    val = pfn_to_paddr(ctxt_entry[devfn].slptptr);
>      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 fec969ef75bb..cb057ced3cf7 100644
> --- a/xen/drivers/passthrough/vtd/x86/ats.c
> +++ b/xen/drivers/passthrough/vtd/x86/ats.c
> @@ -76,7 +76,6 @@ static bool device_in_domain(const struct vtd_iommu
> *iommu,
>  {
>      struct root_entry *root_entry, *root_entries;
>      struct context_entry *context_entry, *context_entries = NULL;
> -    unsigned int tt;
>      bool found = false;
> 
>      if ( unlikely(!iommu->root_maddr) )
> @@ -92,11 +91,10 @@ static bool device_in_domain(const struct
> vtd_iommu *iommu,
> 
>      context_entries = map_vtd_domain_page(root_entry->ctp);
>      context_entry = &context_entries[pdev->devfn];
> -    if ( context_domain_id(*context_entry) != did )
> +    if ( context_entry->did != did )
>          goto out;
> 
> -    tt = context_translation_type(*context_entry);
> -    if ( tt != CONTEXT_TT_DEV_IOTLB )
> +    if ( context_entry->tt != CONTEXT_TT_DEV_IOTLB )
>          goto out;
> 
>      found = true;
> --
> 2.20.1