On 3/22/21 6:05 PM, Alex Elder wrote:
> 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 <rdun...@infradead.org>
> Signed-off-by: Alex Elder <el...@linaro.org>
Acked-by: Randy Dunlap <rdun...@infradead.org> # build-tested
Thanks.
> ---
> drivers/net/ipa/gsi.c | 11 +++++++----
> drivers/net/ipa/ipa_table.c | 9 ++++++---
> 2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
> index 7f3e338ca7a72..b6355827bf900 100644
> --- 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 988f2c2886b95..4236a50ff03ae 100644
> --- 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);
>
--
~Randy
