net: ipa: avoid 64-bit modulus

It is possible for a 32 bit x86 build to use a 64 bit DMA address.

There are two remaining spots where the IPA driver does a modulo
operation to check alignment of a DMA address, and under certain
conditions this can lead to a build error on i386 (at least).

The alignment checks we're doing are for power-of-2 values, and this
means the lower 32 bits of the DMA address can be used.  This ensures
both operands to the modulo operator are 32 bits wide.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
index 7f3e338ca7a72c7ff2cfff07ebabf15d0c5c8d3f..b6355827bf900c1d843d65e6b0988e22fbd9dfc3 100644 (file)
--- a/drivers/net/ipa/gsi.c
+++ b/drivers/net/ipa/gsi.c
@@ -1436,15 +1436,18 @@ static void gsi_evt_ring_rx_update(struct gsi_evt_ring *evt_ring, u32 index)
 /* Initialize a ring, including allocating DMA memory for its entries */
 static int gsi_ring_alloc(struct gsi *gsi, struct gsi_ring *ring, u32 count)
 {
-       size_t size = count * GSI_RING_ELEMENT_SIZE;
+       u32 size = count * GSI_RING_ELEMENT_SIZE;
        struct device *dev = gsi->dev;
        dma_addr_t addr;
 
-       /* Hardware requires a 2^n ring size, with alignment equal to size */
+       /* Hardware requires a 2^n ring size, with alignment equal to size.
+        * The size is a power of 2, so we can check alignment using just
+        * the bottom 32 bits for a DMA address of any size.
+        */
        ring->virt = dma_alloc_coherent(dev, size, &addr, GFP_KERNEL);
-       if (ring->virt && addr % size) {
+       if (ring->virt && lower_32_bits(addr) % size) {
                dma_free_coherent(dev, size, ring->virt, addr);
-               dev_err(dev, "unable to alloc 0x%zx-aligned ring buffer\n",
+               dev_err(dev, "unable to alloc 0x%x-aligned ring buffer\n",
                        size);
                return -EINVAL; /* Not a good error value, but distinct */
        } else if (!ring->virt) {

diff --git a/drivers/net/ipa/ipa_table.c b/drivers/net/ipa/ipa_table.c
index 988f2c2886b9536b788811483b0f615d90043319..4236a50ff03aead302cb277cb07ac33f125e9afd 100644 (file)
--- a/drivers/net/ipa/ipa_table.c
+++ b/drivers/net/ipa/ipa_table.c
@@ -658,10 +658,13 @@ int ipa_table_init(struct ipa *ipa)
                return -ENOMEM;
 
        /* We put the "zero rule" at the base of our table area.  The IPA
-        * hardware requires rules to be aligned on a 128-byte boundary.
-        * Make sure the allocation satisfies this constraint.
+        * hardware requires route and filter table rules to be aligned
+        * on a 128-byte boundary.  As long as the alignment constraint
+        * is a power of 2, we can check alignment using just the bottom
+        * 32 bits for a DMA address of any size.
         */
-       if (addr % IPA_TABLE_ALIGN) {
+       BUILD_BUG_ON(!is_power_of_2(IPA_TABLE_ALIGN));
+       if (lower_32_bits(addr) % IPA_TABLE_ALIGN) {
                dev_err(dev, "table address %pad not %u-byte aligned\n",
                        &addr, IPA_TABLE_ALIGN);
                dma_free_coherent(dev, size, virt, addr);