diff --git a/xen/arch/x86/guest/xen/xen.c b/xen/arch/x86/guest/xen/xen.c
index d9768cc9527d..7484b3f73ad3 100644
--- a/xen/arch/x86/guest/xen/xen.c
+++ b/xen/arch/x86/guest/xen/xen.c
@@ -168,14 +168,14 @@ static void cf_check xen_evtchn_upcall(void)
 
     while ( pending )
     {
-        unsigned int l1 = find_first_set_bit(pending);
+        unsigned int l1 = ffsl(pending) - 1;
         unsigned long evtchn = xchg(&XEN_shared_info->evtchn_pending[l1], 0);
 
         __clear_bit(l1, &pending);
         evtchn &= ~XEN_shared_info->evtchn_mask[l1];
         while ( evtchn )
         {
-            unsigned int port = find_first_set_bit(evtchn);
+            unsigned int port = ffsl(evtchn) - 1;
 
             __clear_bit(port, &evtchn);
             port += l1 * BITS_PER_LONG;
diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index b0cb96c3bc76..68c08bbe94f7 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -139,7 +139,7 @@ static int __init pvh_populate_memory_range(struct domain *d,
         order = get_order_from_pages(end - start + 1);
         order = min(order ? order - 1 : 0, max_order);
         /* The order allocated and populated must be aligned to the address. */
-        order = min(order, start ? find_first_set_bit(start) : MAX_ORDER);
+        order = min(order, start ? ffsl(start) - 1 : MAX_ORDER);
         page = alloc_domheap_pages(d, order, dom0_memflags | MEMF_no_scrub);
         if ( page == NULL )
         {
diff --git a/xen/arch/x86/hvm/hpet.c b/xen/arch/x86/hvm/hpet.c
index 12b00b770257..37e765e97df9 100644
--- a/xen/arch/x86/hvm/hpet.c
+++ b/xen/arch/x86/hvm/hpet.c
@@ -335,7 +335,7 @@ static void timer_sanitize_int_route(HPETState *h, unsigned int tn)
      * enabled pick the first irq.
      */
     timer_config(h, tn) |=
-        MASK_INSR(find_first_set_bit(timer_int_route_cap(h, tn)),
+        MASK_INSR(ffsl(timer_int_route_cap(h, tn)) - 1,
                   HPET_TN_ROUTE);
 }
 
@@ -409,7 +409,7 @@ static int cf_check hpet_write(
         {
             bool active;
 
-            i = find_first_set_bit(new_val);
+            i = ffsl(new_val) - 1;
             if ( i >= HPET_TIMER_NUM )
                 break;
             __clear_bit(i, &new_val);
@@ -535,14 +535,14 @@ static int cf_check hpet_write(
     /* stop/start timers whos state was changed by this write. */
     while (stop_timers)
     {
-        i = find_first_set_bit(stop_timers);
+        i = ffsl(stop_timers) - 1;
         __clear_bit(i, &stop_timers);
         hpet_stop_timer(h, i, guest_time);
     }
 
     while (start_timers)
     {
-        i = find_first_set_bit(start_timers);
+        i = ffsl(start_timers) - 1;
         __clear_bit(i, &start_timers);
         hpet_set_timer(h, i, guest_time);
     }
diff --git a/xen/arch/x86/include/asm/pt-contig-markers.h b/xen/arch/x86/include/asm/pt-contig-markers.h
index b3c1fe803534..e8c8157d605f 100644
--- a/xen/arch/x86/include/asm/pt-contig-markers.h
+++ b/xen/arch/x86/include/asm/pt-contig-markers.h
@@ -60,7 +60,7 @@ static bool pt_update_contig_markers(uint64_t *pt, unsigned int idx,
     /* Step 1: Reduce markers in lower numbered entries. */
     while ( i )
     {
-        b = find_first_set_bit(i);
+        b = ffsl(i) - 1;
         i &= ~(1U << b);
         if ( GET_MARKER(pt[i]) <= b )
             break;
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index d968bbbc7315..2a84bdae670b 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3424,7 +3424,7 @@ static int vcpumask_to_pcpumask(
         {
             unsigned int cpu;
 
-            vcpu_id = find_first_set_bit(vmask);
+            vcpu_id = ffsl(vmask) - 1;
             vmask &= ~(1UL << vcpu_id);
             vcpu_id += vcpu_bias;
             if ( (vcpu_id >= d->max_vcpus) )
diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index 1c727c78c833..bd84fe9e27ee 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -684,7 +684,7 @@ unsigned long
 p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, unsigned int order)
 {
     unsigned long left = 1UL << order, ret = 0;
-    unsigned int chunk_order = find_first_set_bit(gfn_x(gfn) | left);
+    unsigned int chunk_order = ffsl(gfn_x(gfn) | left) - 1;
 
     do {
         ret += decrease_reservation(d, gfn, chunk_order);
@@ -1393,7 +1393,7 @@ guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn,
                                       unsigned int order)
 {
     unsigned long left = 1UL << order;
-    unsigned int chunk_order = find_first_set_bit(gfn | left);
+    unsigned int chunk_order = ffsl(gfn | left) - 1;
     int rc;
 
     if ( !paging_mode_translate(d) )
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 8d3342e95236..054b7edb3989 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1819,7 +1819,7 @@ static void _init_heap_pages(const struct page_info *pg,
     if ( unlikely(!avail[nid]) )
     {
         bool use_tail = IS_ALIGNED(s, 1UL << MAX_ORDER) &&
-                        (find_first_set_bit(e) <= find_first_set_bit(s));
+                        (ffsl(e) <= ffsl(s));
         unsigned long n;
 
         n = init_node_heap(nid, s, nr_pages, &use_tail);
diff --git a/xen/common/softirq.c b/xen/common/softirq.c
index 321d26902d37..bee4a82009c3 100644
--- a/xen/common/softirq.c
+++ b/xen/common/softirq.c
@@ -48,7 +48,7 @@ static void __do_softirq(unsigned long ignore_mask)
              || cpu_is_offline(cpu) )
             break;
 
-        i = find_first_set_bit(pending);
+        i = ffsl(pending) - 1;
         clear_bit(i, &softirq_pending(cpu));
         (*softirq_handlers[i])();
     }
diff --git a/xen/drivers/passthrough/amd/iommu_map.c b/xen/drivers/passthrough/amd/iommu_map.c
index e0f4fe736a8d..f1061bfc798c 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -137,7 +137,7 @@ static void set_iommu_ptes_present(unsigned long pt_mfn,
         ASSERT(!pde->u);
 
         if ( pde > table )
-            ASSERT(pde->ign0 == find_first_set_bit(pde - table));
+            ASSERT(pde->ign0 == ffsl(pde - table) - 1);
         else
             ASSERT(pde->ign0 == CONTIG_LEVEL_SHIFT);
 
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index ba18136c461c..50bfd62553ae 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -305,7 +305,7 @@ static unsigned int mapping_order(const struct domain_iommu *hd,
 {
     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;
+    unsigned int bit = ffsl(sizes) - 1, order = 0;
 
     ASSERT(bit == PAGE_SHIFT);
 
@@ -313,7 +313,7 @@ static unsigned int mapping_order(const struct domain_iommu *hd,
     {
         unsigned long mask;
 
-        bit = find_first_set_bit(sizes);
+        bit = ffsl(sizes) - 1;
         mask = (1UL << bit) - 1;
         if ( nr <= mask || (res & mask) )
             break;
diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c
index 304a2f5480c7..cc0062b02712 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -641,7 +641,7 @@ struct page_info *iommu_alloc_pgtable(struct domain_iommu *hd,
     if ( contig_mask )
     {
         /* See pt-contig-markers.h for a description of the marker scheme. */
-        unsigned int i, shift = find_first_set_bit(contig_mask);
+        unsigned int i, shift = ffsl(contig_mask) - 1;
 
         ASSERT((CONTIG_LEVEL_SHIFT & (contig_mask >> shift)) == CONTIG_LEVEL_SHIFT);
 
@@ -652,7 +652,7 @@ struct page_info *iommu_alloc_pgtable(struct domain_iommu *hd,
 
         for ( i = 4; i < PAGE_SIZE / sizeof(*p); i += 4 )
         {
-            p[i + 0] = (find_first_set_bit(i) + 0ULL) << shift;
+            p[i + 0] = (ffsl(i) - 1ULL) << shift;
             p[i + 1] = 0;
             p[i + 2] = 1ULL << shift;
             p[i + 3] = 0;
