IOMMU: have iommu_{,un}map() split requests into largest possible chunks

Introduce a helper function to determine the largest possible mapping
that allows covering a request (or the next part of it that is left to
be processed).

In order to not add yet more recurring dfn_add() / mfn_add() to the two
callers of the new helper, also introduce local variables holding the
values presently operated on.

Note that strictly speaking iommu_unmap() doen't need to consult
mapping_order(), as unmapping doesn't require superpage support. This,
however, prevents freeing of deep hierarchies of page tables in vendor
code (once suitably enabled), which otherwise would require dealing with
preemption needs.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

xen/drivers/passthrough/iommu.c

@@ -283,12 +283,38 @@ void iommu_domain_destroy(struct domain *d)
     arch_iommu_domain_destroy(d);
 }
 
-int iommu_map(struct domain *d, dfn_t dfn, mfn_t mfn,
+static unsigned int mapping_order(const struct domain_iommu *hd,
+                                  dfn_t dfn, mfn_t mfn, unsigned long nr)
+{
+    unsigned long res = dfn_x(dfn) | mfn_x(mfn);
+    unsigned long sizes = hd->platform_ops->page_sizes;
+    unsigned int bit = find_first_set_bit(sizes), order = 0;
+
+    ASSERT(bit == PAGE_SHIFT);
+
+    while ( (sizes = (sizes >> bit) & ~1) )
+    {
+        unsigned long mask;
+
+        bit = find_first_set_bit(sizes);
+        mask = (1UL << bit) - 1;
+        if ( nr <= mask || (res & mask) )
+            break;
+        order += bit;
+        nr >>= bit;
+        res >>= bit;
+    }
+
+    return order;
+}
+
+int iommu_map(struct domain *d, dfn_t dfn0, mfn_t mfn0,
               unsigned long page_count, unsigned int flags,
               unsigned int *flush_flags)
 {
     const struct domain_iommu *hd = dom_iommu(d);
     unsigned long i;
+    unsigned int order;
     int rc = 0;
 
     if ( !is_iommu_enabled(d) )
@@ -296,10 +322,15 @@ int iommu_map(struct domain *d, dfn_t dfn, mfn_t mfn,
 
     ASSERT(!IOMMUF_order(flags));
 
-    for ( i = 0; i < page_count; i++ )
+    for ( i = 0; i < page_count; i += 1UL << order )
     {
-        rc = iommu_call(hd->platform_ops, map_page, d, dfn_add(dfn, i),
-                        mfn_add(mfn, i), flags, flush_flags);
+        dfn_t dfn = dfn_add(dfn0, i);
+        mfn_t mfn = mfn_add(mfn0, i);
+
+        order = mapping_order(hd, dfn, mfn, page_count - i);
+
+        rc = iommu_call(hd->platform_ops, map_page, d, dfn, mfn,
+                        flags | IOMMUF_order(order), flush_flags);
 
         if ( likely(!rc) )
             continue;
@@ -307,11 +338,10 @@ int iommu_map(struct domain *d, dfn_t dfn, mfn_t mfn,
         if ( !d->is_shutting_down && printk_ratelimit() )
             printk(XENLOG_ERR
                    "d%d: IOMMU mapping dfn %"PRI_dfn" to mfn %"PRI_mfn" failed: %d\n",
-                   d->domain_id, dfn_x(dfn_add(dfn, i)),
-                   mfn_x(mfn_add(mfn, i)), rc);
+                   d->domain_id, dfn_x(dfn), mfn_x(mfn), rc);
 
         /* while statement to satisfy __must_check */
-        while ( iommu_unmap(d, dfn, i, flush_flags) )
+        while ( iommu_unmap(d, dfn0, i, flush_flags) )
             break;
 
         if ( !is_hardware_domain(d) )
@@ -343,20 +373,25 @@ int iommu_legacy_map(struct domain *d, dfn_t dfn, mfn_t mfn,
     return rc;
 }
 
-int iommu_unmap(struct domain *d, dfn_t dfn, unsigned long page_count,
+int iommu_unmap(struct domain *d, dfn_t dfn0, unsigned long page_count,
                 unsigned int *flush_flags)
 {
     const struct domain_iommu *hd = dom_iommu(d);
     unsigned long i;
+    unsigned int order;
     int rc = 0;
 
     if ( !is_iommu_enabled(d) )
         return 0;
 
-    for ( i = 0; i < page_count; i++ )
+    for ( i = 0; i < page_count; i += 1UL << order )
     {
-        int err = iommu_call(hd->platform_ops, unmap_page, d, dfn_add(dfn, i),
-                             0, flush_flags);
+        dfn_t dfn = dfn_add(dfn0, i);
+        int err;
+
+        order = mapping_order(hd, dfn, _mfn(0), page_count - i);
+        err = iommu_call(hd->platform_ops, unmap_page, d, dfn,
+                         order, flush_flags);
 
         if ( likely(!err) )
             continue;
@@ -364,7 +399,7 @@ int iommu_unmap(struct domain *d, dfn_t dfn, unsigned long page_count,
         if ( !d->is_shutting_down && printk_ratelimit() )
             printk(XENLOG_ERR
                    "d%d: IOMMU unmapping dfn %"PRI_dfn" failed: %d\n",
-                   d->domain_id, dfn_x(dfn_add(dfn, i)), err);
+                   d->domain_id, dfn_x(dfn), err);
 
         if ( !rc )
             rc = err;