Re: [Xen-devel] [RFC 21/22] xen/arm: p2m: Re-implement p2m_set_mem_access using p2m_{set, get}_entry

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 28 Jul 2016, Julien Grall wrote:
> The function p2m_set_mem_access can be re-implemented using the generic
> functions p2m_get_entry and __p2m_set_entry.
> 
> Note that because of the implementation of p2m_get_entry, a TLB
> invalidation instruction will be issued for each 4KB page. Therefore the
> performance of memaccess will be impacted, however the function is now
> safe on all the processors.
> 
> Also the function apply_p2m_changes is dropped completely as it is not
> unused anymore.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


>     I have not ran any performance test with memaccess for now, but I
>     expect an important and unavoidable impact because of how memaccess
>     has been designed to workaround hardware limitation. Note that might
>     be possible to re-work memaccess work on superpage but this should
>     be done in a separate patch.
> ---
>  xen/arch/arm/p2m.c | 329 
> +++++++----------------------------------------------
>  1 file changed, 38 insertions(+), 291 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 707c7be..16ed393 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1081,295 +1081,6 @@ static int p2m_set_entry(struct p2m_domain *p2m,
>      return rc;
>  }
>  
> -#define P2M_ONE_DESCEND        0
> -#define P2M_ONE_PROGRESS_NOP   0x1
> -#define P2M_ONE_PROGRESS       0x10
> -
> -static int p2m_shatter_page(struct p2m_domain *p2m,
> -                            lpae_t *entry,
> -                            unsigned int level)
> -{
> -    const paddr_t level_shift = level_shifts[level];
> -    int rc = p2m_create_table(p2m, entry, level_shift - PAGE_SHIFT);
> -
> -    if ( !rc )
> -    {
> -        p2m->stats.shattered[level]++;
> -        p2m->stats.mappings[level]--;
> -        p2m->stats.mappings[level+1] += LPAE_ENTRIES;
> -    }
> -
> -    return rc;
> -}
> -
> -/*
> - * 0   == (P2M_ONE_DESCEND) continue to descend the tree
> - * +ve == (P2M_ONE_PROGRESS_*) handled at this level, continue, flush,
> - *        entry, addr and maddr updated.  Return value is an
> - *        indication of the amount of work done (for preemption).
> - * -ve == (-Exxx) error.
> - */
> -static int apply_one_level(struct domain *d,
> -                           lpae_t *entry,
> -                           unsigned int level,
> -                           enum p2m_operation op,
> -                           paddr_t start_gpaddr,
> -                           paddr_t end_gpaddr,
> -                           paddr_t *addr,
> -                           paddr_t *maddr,
> -                           bool_t *flush,
> -                           p2m_type_t t,
> -                           p2m_access_t a)
> -{
> -    const paddr_t level_size = level_sizes[level];
> -
> -    struct p2m_domain *p2m = &d->arch.p2m;
> -    lpae_t pte;
> -    const lpae_t orig_pte = *entry;
> -    int rc;
> -
> -    BUG_ON(level > 3);
> -
> -    switch ( op )
> -    {
> -    case MEMACCESS:
> -        if ( level < 3 )
> -        {
> -            if ( !p2m_valid(orig_pte) )
> -            {
> -                *addr += level_size;
> -                return P2M_ONE_PROGRESS_NOP;
> -            }
> -
> -            /* Shatter large pages as we descend */
> -            if ( p2m_mapping(orig_pte) )
> -            {
> -                rc = p2m_shatter_page(p2m, entry, level);
> -                if ( rc < 0 )
> -                    return rc;
> -            } /* else: an existing table mapping -> descend */
> -
> -            return P2M_ONE_DESCEND;
> -        }
> -        else
> -        {
> -            pte = orig_pte;
> -
> -            if ( p2m_valid(pte) )
> -            {
> -                rc = p2m_mem_access_radix_set(p2m, _gfn(paddr_to_pfn(*addr)),
> -                                              a);
> -                if ( rc < 0 )
> -                    return rc;
> -
> -                p2m_set_permission(&pte, pte.p2m.type, a);
> -                p2m_write_pte(entry, pte, p2m->clean_pte);
> -            }
> -
> -            *addr += level_size;
> -            *flush = true;
> -            return P2M_ONE_PROGRESS;
> -        }
> -    }
> -
> -    BUG(); /* Should never get here */
> -}
> -
> -/*
> - * The page is only used by the P2M code which is protected by the p2m->lock.
> - * So we can avoid to use atomic helpers.
> - */
> -static void update_reference_mapping(struct page_info *page,
> -                                     lpae_t old_entry,
> -                                     lpae_t new_entry)
> -{
> -    if ( p2m_valid(old_entry) && !p2m_valid(new_entry) )
> -        page->u.inuse.p2m_refcount--;
> -    else if ( !p2m_valid(old_entry) && p2m_valid(new_entry) )
> -        page->u.inuse.p2m_refcount++;
> -}
> -
> -static int apply_p2m_changes(struct domain *d,
> -                     enum p2m_operation op,
> -                     gfn_t sgfn,
> -                     unsigned long nr,
> -                     mfn_t smfn,
> -                     uint32_t mask,
> -                     p2m_type_t t,
> -                     p2m_access_t a)
> -{
> -    paddr_t start_gpaddr = pfn_to_paddr(gfn_x(sgfn));
> -    paddr_t end_gpaddr = pfn_to_paddr(gfn_x(sgfn) + nr);
> -    paddr_t maddr = pfn_to_paddr(mfn_x(smfn));
> -    int rc, ret;
> -    struct p2m_domain *p2m = &d->arch.p2m;
> -    lpae_t *mappings[4] = { NULL, NULL, NULL, NULL };
> -    struct page_info *pages[4] = { NULL, NULL, NULL, NULL };
> -    paddr_t addr;
> -    unsigned int level = 0;
> -    unsigned int cur_root_table = ~0;
> -    unsigned int cur_offset[4] = { ~0, ~0, ~0, ~0 };
> -    unsigned int count = 0;
> -    const unsigned int preempt_count_limit = (op == MEMACCESS) ? 1 : 0x2000;
> -    const bool_t preempt = !is_idle_vcpu(current);
> -    bool_t flush = false;
> -    PAGE_LIST_HEAD(free_pages);
> -    struct page_info *pg;
> -
> -    p2m_write_lock(p2m);
> -
> -    /* Static mapping. P2M_ROOT_PAGES > 1 are handled below */
> -    if ( P2M_ROOT_PAGES == 1 )
> -    {
> -        mappings[P2M_ROOT_LEVEL] = __map_domain_page(p2m->root);
> -        pages[P2M_ROOT_LEVEL] = p2m->root;
> -    }
> -
> -    addr = start_gpaddr;
> -    while ( addr < end_gpaddr )
> -    {
> -        int root_table;
> -        const unsigned int offsets[4] = {
> -            zeroeth_table_offset(addr),
> -            first_table_offset(addr),
> -            second_table_offset(addr),
> -            third_table_offset(addr)
> -        };
> -
> -        /*
> -         * Check if current iteration should be possibly preempted.
> -         * Since count is initialised to 0 above we are guaranteed to
> -         * always make at least one pass as long as preempt_count_limit is
> -         * initialized with a value >= 1.
> -         */
> -        if ( preempt && count >= preempt_count_limit
> -             && hypercall_preempt_check() )
> -        {
> -            switch ( op )
> -            {
> -            case MEMACCESS:
> -            {
> -                /*
> -                 * Preempt setting mem_access permissions as required by 
> XSA-89,
> -                 * if it's not the last iteration.
> -                 */
> -                uint32_t progress = paddr_to_pfn(addr) - gfn_x(sgfn) + 1;
> -
> -                if ( nr > progress && !(progress & mask) )
> -                {
> -                    rc = progress;
> -                    goto out;
> -                }
> -                break;
> -            }
> -
> -            default:
> -                break;
> -            };
> -
> -            /*
> -             * Reset current iteration counter.
> -             */
> -            count = 0;
> -        }
> -
> -        if ( P2M_ROOT_PAGES > 1 )
> -        {
> -            int i;
> -            /*
> -             * Concatenated root-level tables. The table number will be the
> -             * offset at the previous level. It is not possible to 
> concatenate
> -             * a level-0 root.
> -             */
> -            ASSERT(P2M_ROOT_LEVEL > 0);
> -            root_table = offsets[P2M_ROOT_LEVEL - 1];
> -            if ( root_table >= P2M_ROOT_PAGES )
> -            {
> -                rc = -EINVAL;
> -                goto out;
> -            }
> -
> -            if ( cur_root_table != root_table )
> -            {
> -                if ( mappings[P2M_ROOT_LEVEL] )
> -                    unmap_domain_page(mappings[P2M_ROOT_LEVEL]);
> -                mappings[P2M_ROOT_LEVEL] =
> -                    __map_domain_page(p2m->root + root_table);
> -                pages[P2M_ROOT_LEVEL] = p2m->root + root_table;
> -                cur_root_table = root_table;
> -                /* Any mapping further down is now invalid */
> -                for ( i = P2M_ROOT_LEVEL; i < 4; i++ )
> -                    cur_offset[i] = ~0;
> -            }
> -        }
> -
> -        for ( level = P2M_ROOT_LEVEL; level < 4; level++ )
> -        {
> -            unsigned offset = offsets[level];
> -            lpae_t *entry = &mappings[level][offset];
> -            lpae_t old_entry = *entry;
> -
> -            ret = apply_one_level(d, entry,
> -                                  level, op,
> -                                  start_gpaddr, end_gpaddr,
> -                                  &addr, &maddr, &flush,
> -                                  t, a);
> -            if ( ret < 0 ) { rc = ret ; goto out; }
> -            count += ret;
> -
> -            if ( ret != P2M_ONE_PROGRESS_NOP )
> -                update_reference_mapping(pages[level], old_entry, *entry);
> -
> -            /* L3 had better have done something! We cannot descend any 
> further */
> -            BUG_ON(level == 3 && ret == P2M_ONE_DESCEND);
> -            if ( ret != P2M_ONE_DESCEND ) break;
> -
> -            BUG_ON(!p2m_valid(*entry));
> -
> -            if ( cur_offset[level] != offset )
> -            {
> -                /* Update mapping for next level */
> -                int i;
> -                if ( mappings[level+1] )
> -                    unmap_domain_page(mappings[level+1]);
> -                mappings[level+1] = map_domain_page(_mfn(entry->p2m.base));
> -                pages[level+1] = mfn_to_page(entry->p2m.base);
> -                cur_offset[level] = offset;
> -                /* Any mapping further down is now invalid */
> -                for ( i = level+1; i < 4; i++ )
> -                    cur_offset[i] = ~0;
> -            }
> -            /* else: next level already valid */
> -        }
> -
> -        BUG_ON(level > 3);
> -    }
> -
> -    rc = 0;
> -
> -out:
> -    if ( flush )
> -    {
> -        p2m_flush_tlb_sync(&d->arch.p2m);
> -        ret = iommu_iotlb_flush(d, gfn_x(sgfn), nr);
> -        if ( !rc )
> -            rc = ret;
> -    }
> -
> -    while ( (pg = page_list_remove_head(&free_pages)) )
> -        free_domheap_page(pg);
> -
> -    for ( level = P2M_ROOT_LEVEL; level < 4; level ++ )
> -    {
> -        if ( mappings[level] )
> -            unmap_domain_page(mappings[level]);
> -    }
> -
> -    p2m_write_unlock(p2m);
> -
> -    return rc;
> -}
> -
>  static inline int p2m_insert_mapping(struct domain *d,
>                                       gfn_t start_gfn,
>                                       unsigned long nr,
> @@ -2069,6 +1780,7 @@ long p2m_set_mem_access(struct domain *d, gfn_t gfn, 
> uint32_t nr,
>  {
>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
>      p2m_access_t a;
> +    unsigned int order;
>      long rc = 0;
>  
>      static const p2m_access_t memaccess[] = {
> @@ -2111,8 +1823,43 @@ long p2m_set_mem_access(struct domain *d, gfn_t gfn, 
> uint32_t nr,
>          return 0;
>      }
>  
> -    rc = apply_p2m_changes(d, MEMACCESS, gfn_add(gfn, start),
> -                           (nr - start), INVALID_MFN, mask, 0, a);
> +    p2m_write_lock(p2m);
> +
> +    for ( gfn = gfn_add(gfn, start); nr > start; gfn = gfn_add(gfn, 1UL << 
> order) )
> +    {
> +        p2m_type_t t;
> +        mfn_t mfn = p2m_get_entry(p2m, gfn, &t, NULL, &order);
> +
> +        /* Skip hole */
> +        if ( mfn_eq(mfn, INVALID_MFN) )
> +        {
> +            /*
> +             * the order corresponds to the order of the mapping in the
> +             * page table. so we need to align the gfn before
> +             * incrementing.
> +             */
> +            gfn = _gfn(gfn_x(gfn) & ~((1UL << order) - 1));
> +            continue;
> +        }
> +        else
> +        {
> +            order = 0;
> +            rc = __p2m_set_entry(p2m, gfn, 0, mfn, t, a);
> +            if ( rc )
> +                break;
> +        }
> +
> +        start += (1UL << order);
> +        /* Check for continuation if it is not the last iteration */
> +        if ( nr > start && !(start & mask) && hypercall_preempt_check() )
> +        {
> +            rc = start;
> +            break;
> +        }
> +    }
> +
> +    p2m_write_unlock(p2m);
> +
>      if ( rc < 0 )
>          return rc;
>      else if ( rc > 0 )
.9.1


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