Re: [Xen-devel] RFC: AMD support for paging

[Hongkaixing <hongkaixing@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Andres 
> Lagar-Cavilla
> Sent: Wednesday, February 15, 2012 3:05 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: olaf@xxxxxxxxx; keir.xen@xxxxxxxxx; tim@xxxxxxx; JBeulich@xxxxxxxx; 
> adin@xxxxxxxxxxxxxx
> Subject: [Xen-devel] RFC: AMD support for paging
> 
> We started hashing out some AMD support for mem_paging and mem_access.
> Right now my VMs boot, page out a bit, and then die on an HVM triple
> fault.
> 
> Most importantly, I want to get somebody from AMD to comment/help out on
> this. It feels like we're inches away from enabling support for this very
> nice feature. I'm not sure who exactly on AMD monitors the list for these
> kinds of things. It'd be great to have you on board!
> 
> For starters, the changes to the p2m code are relatively mild, but it'd be
> great if somebody spots a red flag.
> 
> Another issue: comments indicate that bits 59-62 in NPT entries are used
> for IOMMU flags but effectively bits 61-62 are. Repossessing one bit (59)
> would give us enough space to support mem_access. Right now we only have 7
> bits available for Xen flags and that is not enough for paging and access.
> Is bit 59 effectively reserved?
> 
> Finally, the triple fault. Maybe I'm missing something obvious. Comments
> welcome.
> 
> Patch inline below, thanks!
> Andres
> 
> Enable AMD support for paging.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
> Signed-off-by: Adin Scannell <adin@xxxxxxxxxxx>
> 
> diff -r 25ca78889ed4 -r 10ca4e4293ce xen/arch/x86/mm/mem_event.c
> --- a/xen/arch/x86/mm/mem_event.c
> +++ b/xen/arch/x86/mm/mem_event.c
> @@ -537,10 +537,6 @@ int mem_event_domctl(struct domain *d, x
>              if ( !hap_enabled(d) )
>                  break;
> 
> -            /* Currently only EPT is supported */
> -            if ( boot_cpu_data.x86_vendor != X86_VENDOR_INTEL )
> -                break;
> -
>              rc = -EXDEV;
>              /* Disallow paging in a PoD guest */
>              if ( p2m->pod.entry_count )
> diff -r 25ca78889ed4 -r 10ca4e4293ce xen/arch/x86/mm/p2m-pt.c
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -53,6 +53,20 @@
>  #define P2M_BASE_FLAGS \
>          (_PAGE_PRESENT | _PAGE_USER | _PAGE_DIRTY | _PAGE_ACCESSED)
> 
> +#ifdef __x86_64__
> +/* l1e_from_pfn is not designed to have INVALID_MFN stored. The 0xff..ff
> + * value tramples over the higher-order bits used for flags (NX, p2mt,
> + * etc.) This happens for paging entries. Thus we do this clip/unclip
> + * juggle for l1 entries only (no paging superpages!) */
> +#define EFF_MFN_WIDTH       (PADDR_BITS-PAGE_SHIFT) /* 40 bits */
> +#define clipped_mfn(mfn)    ((mfn) & ((1UL << EFF_MFN_WIDTH) - 1))
> +#define unclip_mfn(mfn)     ((clipped_mfn((mfn)) == INVALID_MFN) ? \
> +                                INVALID_MFN : (mfn))
> +#else
> +#define clipped_mfn(mfn)    (mfn)
> +#define unclip_mfn(mfn)     (mfn)
> +#endif /* __x86_64__ */
> +
>  static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn)
>  {
>      unsigned long flags;
> @@ -77,6 +91,9 @@ static unsigned long p2m_type_to_flags(p
>      case p2m_invalid:
>      case p2m_mmio_dm:
>      case p2m_populate_on_demand:
> +    case p2m_ram_paging_out:
> +    case p2m_ram_paged:
> +    case p2m_ram_paging_in:
>      default:
>          return flags;
>      case p2m_ram_ro:
> @@ -168,7 +185,7 @@ p2m_next_level(struct p2m_domain *p2m, m
>                                        shift, max)) )
>          return 0;
> 
> -    /* PoD: Not present doesn't imply empty. */
> +    /* PoD/paging: Not present doesn't imply empty. */
>      if ( !l1e_get_flags(*p2m_entry) )
>      {
>          struct page_info *pg;
> @@ -384,8 +401,9 @@ p2m_set_entry(struct p2m_domain *p2m, un
>                                     0, L1_PAGETABLE_ENTRIES);
>          ASSERT(p2m_entry);
> 
> -        if ( mfn_valid(mfn) || (p2mt == p2m_mmio_direct) )
> -            entry_content = l1e_from_pfn(mfn_x(mfn),
> +        if ( mfn_valid(mfn) || (p2mt == p2m_mmio_direct) ||
> +             (p2mt == p2m_ram_paged) || (p2mt == p2m_ram_paging_in) )
> +            entry_content = l1e_from_pfn(clipped_mfn(mfn_x(mfn)),
>                                           p2m_type_to_flags(p2mt, mfn));
>          else
>              entry_content = l1e_empty();
> @@ -393,7 +411,7 @@ p2m_set_entry(struct p2m_domain *p2m, un
>          if ( entry_content.l1 != 0 )
>          {
>              p2m_add_iommu_flags(&entry_content, 0, iommu_pte_flags);
> -            old_mfn = l1e_get_pfn(*p2m_entry);
> +            old_mfn = unclip_mfn(l1e_get_pfn(*p2m_entry));
>          }
>          /* level 1 entry */
>          p2m->write_p2m_entry(p2m, gfn, p2m_entry, table_mfn,
> entry_content, 1);
> @@ -615,11 +633,12 @@ pod_retry_l1:
>                             sizeof(l1e));
> 
>      if ( ret == 0 ) {
> +        unsigned long l1e_mfn = unclip_mfn(l1e_get_pfn(l1e));
>          p2mt = p2m_flags_to_type(l1e_get_flags(l1e));
> -        ASSERT(l1e_get_pfn(l1e) != INVALID_MFN || !p2m_is_ram(p2mt));
> +        ASSERT( (l1e_mfn != INVALID_MFN || !p2m_is_ram(p2mt)) ||
> +                (l1e_mfn == INVALID_MFN && p2m_is_paging(p2mt)) );
> 
> -        if ( p2m_flags_to_type(l1e_get_flags(l1e))
> -             == p2m_populate_on_demand )
> +        if ( p2mt == p2m_populate_on_demand )
>          {
>              /* The read has succeeded, so we know that the mapping
>               * exits at this point.  */
> @@ -641,7 +660,7 @@ pod_retry_l1:
>          }
> 
>          if ( p2m_is_valid(p2mt) || p2m_is_grant(p2mt) )
> -            mfn = _mfn(l1e_get_pfn(l1e));
> +            mfn = _mfn(l1e_mfn);
>          else
>              /* XXX see above */
>              p2mt = p2m_mmio_dm;
> @@ -783,18 +802,26 @@ pod_retry_l2:
>  pod_retry_l1:
>      if ( (l1e_get_flags(*l1e) & _PAGE_PRESENT) == 0 )
>      {
> +        p2m_type_t l1t = p2m_flags_to_type(l1e_get_flags(*l1e));
>          /* PoD: Try to populate */
> -        if ( p2m_flags_to_type(l1e_get_flags(*l1e)) ==
> p2m_populate_on_demand )
> +        if ( l1t == p2m_populate_on_demand )
>          {
>              if ( q != p2m_query ) {
>                  if ( !p2m_pod_demand_populate(p2m, gfn, PAGE_ORDER_4K, q) )
>                      goto pod_retry_l1;
>              } else
>                  *t = p2m_populate_on_demand;
> +        } else {
> +            if ( p2m_is_paging(l1t) )
> +            {
> +                *t = l1t;
> +                /* No need to unclip due to check below */
> +                mfn = _mfn(l1e_get_pfn(*l1e));
> +            }
>          }
> 
>          unmap_domain_page(l1e);
> -        return _mfn(INVALID_MFN);
> +        return (l1t == p2m_ram_paging_out) ? mfn : _mfn(INVALID_MFN);
            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                   This means when p2mt is p2m_ram_paging_in, the mfn must be 
INVALID_MFN;
                   But in p2m_type_to_flags,when p2m_ram_paging_in or  
p2m_ram_paged, the _PAGE_PRESENT is not set.
 
My idea shows like this:
In p2m_gfn_to_mfn function:
@@ -1370,6 +1379,7 @@
     paddr_t addr = ((paddr_t)gfn) << PAGE_SHIFT;
     l2_pgentry_t *l2e;
     l1_pgentry_t *l1e;
+    unsigned long flags;
 
     ASSERT(paging_mode_translate(d));
 
@@ -1455,7 +1465,8 @@
     l1e = map_domain_page(mfn_x(mfn));
     l1e += l1_table_offset(addr);
 pod_retry_l1:
-    if ( (l1e_get_flags(*l1e) & _PAGE_PRESENT) == 0 )
+    flags = l1e_get_flags(*l1e);
+    if ((( flags & _PAGE_PRESENT) == 0) && 
(!p2m_is_paging(p2m_flags_to_type(flags))))
     {
         /* PoD: Try to populate */
         if ( p2m_flags_to_type(l1e_get_flags(*l1e)) == p2m_populate_on_demand )
        {
            if ( q != p2m_query ) {
                if ( !p2m_pod_check_and_populate(p2m, gfn,
                                                 (l1_pgentry_t *)l1e, 
PAGE_ORDER_4K, q) )
                    goto pod_retry_l1;
            } else
                *t = p2m_populate_on_demand;
        }
    
        unmap_domain_page(l1e);
        return _mfn(INVALID_MFN);
    }
    mfn = _mfn(l1e_get_pfn(*l1e));
    *t = p2m_flags_to_type(l1e_get_flags(*l1e));
    unmap_domain_page(l1e);




>      }
>      mfn = _mfn(l1e_get_pfn(*l1e));
>      *t = p2m_flags_to_type(l1e_get_flags(*l1e));
> @@ -914,7 +941,7 @@ static void p2m_change_type_global(struc
>                      flags = l1e_get_flags(l1e[i1]);
>                      if ( p2m_flags_to_type(flags) != ot )
>                          continue;
> -                    mfn = l1e_get_pfn(l1e[i1]);
> +                    mfn = unclip_mfn(l1e_get_pfn(l1e[i1]));
>                      gfn = i1 + (i2 + (i3
>  #if CONFIG_PAGING_LEVELS >= 4
>                                       + (i4 * L3_PAGETABLE_ENTRIES)
> @@ -923,7 +950,7 @@ static void p2m_change_type_global(struc
>                             * L2_PAGETABLE_ENTRIES) * L1_PAGETABLE_ENTRIES;
>                      /* create a new 1le entry with the new type */
>                      flags = p2m_type_to_flags(nt, _mfn(mfn));
> -                    l1e_content = l1e_from_pfn(mfn, flags);
> +                    l1e_content = l1e_from_pfn(clipped_mfn(mfn), flags);
>                      p2m->write_p2m_entry(p2m, gfn, &l1e[i1],
>                                           l1mfn, l1e_content, 1);
>                  }
> @@ -1073,7 +1100,7 @@ long p2m_pt_audit_p2m(struct p2m_domain
>                                  entry_count++;
>                              continue;
>                          }
> -                        mfn = l1e_get_pfn(l1e[i1]);
> +                        mfn = unclip_mfn(l1e_get_pfn(l1e[i1]));
>                          ASSERT(mfn_valid(_mfn(mfn)));
>                          m2pfn = get_gpfn_from_mfn(mfn);
>                          if ( m2pfn != gfn &&
> 
> 
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