diff --git a/drivers/usb/class/hub/hub.c b/drivers/usb/class/hub/hub.c
index 7476d0ac..1b31e8e7 100644
--- a/drivers/usb/class/hub/hub.c
+++ b/drivers/usb/class/hub/hub.c
@@ -179,8 +179,8 @@ static int hub_enumerate_device(usb_hub_t *hub, uint8_t port)
     if (ret != EOK || !child) {
         plogk("usb-hub: %s port %u enumerate failed: %d\n", hub->device->path, port, ret);
 
-        /* De-power the port to avoid babble on failure. */
-        if (hub->has_individual_power) hub_clear_port_feature(hub->device, port, USB_PORT_FEAT_POWER);
+        /* De-power the port to avoid babble on failure, but not for a device the HCD cannot drive: it is fine, merely unsupported. */
+        if (hub->has_individual_power && ret != -EOPNOTSUPP) hub_clear_port_feature(hub->device, port, USB_PORT_FEAT_POWER);
         return ret ? ret : -EIO;
     }
 
@@ -386,10 +386,16 @@ int usb_hub_probe(usb_interface_t *interface)
           hub->power_good_ms * 2);
     if (!hub->has_individual_power) {
         /* Ganged: one PORT_POWER on port 1 powers all, but QEMU requires per-port. */
-        for (uint8_t port = 1; port <= hub->port_count; port++) hub_set_port_feature(device, port, USB_PORT_FEAT_POWER);
+        for (uint8_t port = 1; port <= hub->port_count; port++) {
+            int power = hub_set_port_feature(device, port, USB_PORT_FEAT_POWER);
+            if (power != EOK) plogk("usb-hub: %s port %u power-on failed: %d\n", device->path, port, power);
+        }
         msleep(((uint32_t)hub->power_good_ms * 2) + USB_HUB_POWER_GOOD_MARGIN_MS);
     } else {
-        for (uint8_t port = 1; port <= hub->port_count; port++) hub_power_on_port(hub, port);
+        for (uint8_t port = 1; port <= hub->port_count; port++) {
+            int power = hub_power_on_port(hub, port);
+            if (power != EOK) plogk("usb-hub: %s port %u power-on failed: %d\n", device->path, port, power);
+        }
     }
 
     /* Status-change interrupt: 1 hub bit + port bits, rounded up. */
diff --git a/drivers/usb/host/ehci/ehci.c b/drivers/usb/host/ehci/ehci.c
index ec4b5754..0eca8a64 100644
--- a/drivers/usb/host/ehci/ehci.c
+++ b/drivers/usb/host/ehci/ehci.c
@@ -94,11 +94,11 @@ static void ehci_write32(volatile uint8_t *base, size_t offset, uint32_t value)
     mmio_write32((base + offset), value);
 }
 
-/* Allocate zeroed DMA memory and return its physical address. */
+/* Allocate zeroed DMA memory below 4 GiB (32-bit pointers) and return its physical address. */
 static void *ehci_dma_alloc(size_t size, uint64_t *physical)
 {
     size_t   count   = (size + PAGE_4K_SIZE - 1) / PAGE_4K_SIZE;
-    uint64_t address = alloc_frames(count);
+    uint64_t address = alloc_frames_dma32(count);
     if (!address) return NULL;
     void *memory = phys_to_virt(address);
     memset(memory, 0, count * PAGE_4K_SIZE);
@@ -245,7 +245,8 @@ static void ehci_unschedule_async(ehci_controller_t *ctrl, int qh_index)
 static int ehci_control(usb_device_t *device, const usb_setup_packet_t *setup, void *buffer, size_t length, uint32_t timeout_ms)
 {
     ehci_controller_t *ctrl = device ? device->hc_private : NULL;
-    if (!ctrl || !setup || device->speed != USB_SPEED_HIGH || (length && !buffer) || length > PAGE_4K_SIZE || length != load_le16(&setup->length)) return -EINVAL;
+    if (ctrl && device->speed != USB_SPEED_HIGH) return -EOPNOTSUPP;
+    if (!ctrl || !setup || (length && !buffer) || length > PAGE_4K_SIZE || length != load_le16(&setup->length)) return -EINVAL;
     uint16_t max_packet = device->descriptor.max_packet_size0 ? device->descriptor.max_packet_size0 : 64;
     if (max_packet != 64) return -EPROTO;
     bool input = (setup->request_type & USB_DIR_IN) != 0;
@@ -329,7 +330,8 @@ static int ehci_transfer(usb_endpoint_t *endpoint, void *buffer, size_t length,
     usb_device_t      *device     = endpoint->interface->device;
     ehci_controller_t *ctrl       = device->hc_private;
     uint16_t           max_packet = load_le16(&endpoint->descriptor.max_packet_size) & 0x07ff;
-    if (!ctrl || device->speed != USB_SPEED_HIGH || !max_packet || max_packet > 1024) return -EINVAL;
+    if (ctrl && device->speed != USB_SPEED_HIGH) return -EOPNOTSUPP;
+    if (!ctrl || !max_packet || max_packet > 1024) return -EINVAL;
     bool    input           = (endpoint->descriptor.endpoint_address & USB_ENDPOINT_DIR_MASK) != 0;
     uint8_t endpoint_number = endpoint->descriptor.endpoint_address & USB_ENDPOINT_NUMBER_MASK;
 
diff --git a/drivers/usb/host/ohci/ohci.c b/drivers/usb/host/ohci/ohci.c
index 5e9a56e1..f2a03dc7 100644
--- a/drivers/usb/host/ohci/ohci.c
+++ b/drivers/usb/host/ohci/ohci.c
@@ -92,11 +92,11 @@ static void ohci_write32(ohci_controller_t *ctrl, uint8_t reg, uint32_t value)
     mmio_write32((uint32_t *)(ctrl->mmio_base + reg), value);
 }
 
-/* Allocate zeroed DMA memory and return its physical address. */
+/* Allocate zeroed DMA memory below 4 GiB (32-bit pointers) and return its physical address. */
 static void *ohci_dma_alloc(size_t size, uint64_t *physical)
 {
     size_t   count   = (size + PAGE_4K_SIZE - 1) / PAGE_4K_SIZE;
-    uint64_t address = alloc_frames(count);
+    uint64_t address = alloc_frames_dma32(count);
     if (!address) return NULL;
     void *memory = phys_to_virt(address);
     memset(memory, 0, count * PAGE_4K_SIZE);
diff --git a/drivers/usb/host/uhci/uhci.c b/drivers/usb/host/uhci/uhci.c
index 0a6773f3..676beba4 100644
--- a/drivers/usb/host/uhci/uhci.c
+++ b/drivers/usb/host/uhci/uhci.c
@@ -121,11 +121,11 @@ static void uhci_writel(uhci_controller_t *ctrl, uint8_t reg, uint32_t value)
     outl(ctrl->io_base + reg, value);
 }
 
-/* Allocate zeroed DMA memory and return its physical address. */
+/* Allocate zeroed DMA memory below 4 GiB (32-bit pointers) and return its physical address. */
 static void *uhci_dma_alloc(size_t size, uint64_t *physical)
 {
     size_t   count   = (size + PAGE_4K_SIZE - 1) / PAGE_4K_SIZE;
-    uint64_t address = alloc_frames(count);
+    uint64_t address = alloc_frames_dma32(count);
     if (!address) return NULL;
     void *memory = phys_to_virt(address);
     memset(memory, 0, count * PAGE_4K_SIZE);
diff --git a/include/mem/buddy.h b/include/mem/buddy.h
index 92a5947e..66080eb6 100644
--- a/include/mem/buddy.h
+++ b/include/mem/buddy.h
@@ -50,6 +50,8 @@ int buddy_add_range(buddy_allocator_t *allocator, size_t start, size_t count);
 
 /* Allocate/free an aligned 2^order-unit block. */
 size_t buddy_alloc(buddy_allocator_t *allocator, unsigned order);
+/* Same, but the whole block must lie below page index limit. */
+size_t buddy_alloc_below(buddy_allocator_t *allocator, unsigned order, size_t limit);
 int    buddy_free(buddy_allocator_t *allocator, size_t index, unsigned order);
 
 /*
diff --git a/include/mem/frame.h b/include/mem/frame.h
index 0c9793db..127aa019 100644
--- a/include/mem/frame.h
+++ b/include/mem/frame.h
@@ -45,6 +45,9 @@ void init_frame(void);
 /* Allocate memory frames */
 uint64_t alloc_frames(size_t count);
 
+/* Allocate memory frames reachable by 32-bit DMA (entirely below 4 GiB) */
+uint64_t alloc_frames_dma32(size_t count);
+
 /* Reclaim pages under the frame allocator's recursion guard. */
 int frame_reclaim_pages(size_t target);
 
diff --git a/mem/buddy.c b/mem/buddy.c
index 50f85aa8..d26ef281 100644
--- a/mem/buddy.c
+++ b/mem/buddy.c
@@ -132,16 +132,9 @@ int buddy_add_range(buddy_allocator_t *allocator, size_t start, size_t count)
     return 0;
 }
 
-/* Allocate a block of the given order, splitting a larger one if needed. */
-size_t buddy_alloc(buddy_allocator_t *allocator, unsigned order)
+/* Carve an allocated block of the given order out of the free block at index. */
+static size_t take_block(buddy_allocator_t *allocator, size_t index, unsigned found, unsigned order)
 {
-    if (!allocator || order > allocator->max_order) return SIZE_MAX;
-
-    unsigned found = order;
-    while (found <= allocator->max_order && allocator->free_head[found] == BUDDY_INDEX_NONE) found++;
-    if (found > allocator->max_order) return SIZE_MAX;
-
-    size_t index = (size_t)allocator->free_head[found];
     list_remove(allocator, index, found);
 
     while (found > order) {
@@ -159,6 +152,33 @@ size_t buddy_alloc(buddy_allocator_t *allocator, unsigned order)
     return index;
 }
 
+/* Allocate a block of the given order, splitting a larger one if needed. */
+size_t buddy_alloc(buddy_allocator_t *allocator, unsigned order)
+{
+    if (!allocator || order > allocator->max_order) return SIZE_MAX;
+
+    unsigned found = order;
+    while (found <= allocator->max_order && allocator->free_head[found] == BUDDY_INDEX_NONE) found++;
+    if (found > allocator->max_order) return SIZE_MAX;
+
+    return take_block(allocator, (size_t)allocator->free_head[found], found, order);
+}
+
+/* Like buddy_alloc(), but the block must end at or below page limit. */
+size_t buddy_alloc_below(buddy_allocator_t *allocator, unsigned order, size_t limit)
+{
+    if (!allocator || order > allocator->max_order) return SIZE_MAX;
+
+    size_t units = order_units(order);
+    for (unsigned found = order; found <= allocator->max_order; found++) {
+        for (int32_t i = allocator->free_head[found]; i != BUDDY_INDEX_NONE; i = allocator->pages[(size_t)i].next) {
+            size_t index = (size_t)i;
+            if (index < limit && limit - index >= units) return take_block(allocator, index, found, order);
+        }
+    }
+    return SIZE_MAX;
+}
+
 /* Return a block of the given order to the allocator. */
 int buddy_free(buddy_allocator_t *allocator, size_t index, unsigned order)
 {
diff --git a/mem/frame.c b/mem/frame.c
index 91668633..05aded34 100644
--- a/mem/frame.c
+++ b/mem/frame.c
@@ -298,15 +298,15 @@ void init_frame(void)
     log_buffer_write(&frame_log, "frame: Available frames after buddy metadata = 0x%08zx (%zu KiB)\n", frame_allocator.usable_frames, (frame_allocator.usable_frames * 4096) >> 10);
 }
 
-/* Allocate count frames aligned to 2^alignment_order pages. */
-static uint64_t alloc_frames_aligned(size_t count, unsigned alignment_order)
+/* Allocate count frames aligned to 2^alignment_order pages, ending below page limit. */
+static uint64_t alloc_frames_limited(size_t count, unsigned alignment_order, size_t limit)
 {
     if (!count) return 0;
     unsigned order = buddy_order_for_units(count);
     if (order > CONFIG_BUDDY_MAX_ORDER) return 0;
     if (alignment_order > order) order = alignment_order;
 
-    if (count == 1 && alignment_order == 0) {
+    if (count == 1 && alignment_order == 0 && limit == SIZE_MAX) {
         size_t frame = frame_pcp_pop();
         if (frame == SIZE_MAX) frame = frame_pcp_refill();
         if (frame == SIZE_MAX) {
@@ -317,12 +317,12 @@ static uint64_t alloc_frames_aligned(size_t count, unsigned alignment_order)
     }
 
     spin_lock(&frame_allocator.lock);
-    size_t frame_index = buddy_alloc(&frame_allocator.buddy, order);
+    size_t frame_index = limit == SIZE_MAX ? buddy_alloc(&frame_allocator.buddy, order) : buddy_alloc_below(&frame_allocator.buddy, order, limit);
     if (frame_index == SIZE_MAX) {
         spin_unlock(&frame_allocator.lock);
         frame_pcp_drain_all();
         spin_lock(&frame_allocator.lock);
-        frame_index = buddy_alloc(&frame_allocator.buddy, order);
+        frame_index = limit == SIZE_MAX ? buddy_alloc(&frame_allocator.buddy, order) : buddy_alloc_below(&frame_allocator.buddy, order, limit);
         if (frame_index == SIZE_MAX) {
             spin_unlock(&frame_allocator.lock);
             return 0;
@@ -340,12 +340,24 @@ static uint64_t alloc_frames_aligned(size_t count, unsigned alignment_order)
     return frame_index * PAGE_4K_SIZE;
 }
 
+/* Allocate count frames aligned to 2^alignment_order pages. */
+static uint64_t alloc_frames_aligned(size_t count, unsigned alignment_order)
+{
+    return alloc_frames_limited(count, alignment_order, SIZE_MAX);
+}
+
 /* Allocate memory frames; reclaim I/O is initiated only at explicit safe points. */
 uint64_t alloc_frames(size_t count)
 {
     return alloc_frames_aligned(count, 0);
 }
 
+/* Allocate memory frames whose physical range lies entirely below 4 GiB. */
+uint64_t alloc_frames_dma32(size_t count)
+{
+    return alloc_frames_limited(count, 0, (size_t)(0x100000000ULL / PAGE_4K_SIZE));
+}
+
 /* Allocate 2M memory frames */
 uint64_t alloc_frames_2M(size_t count)
 {