In the Linux kernel, the following vulnerability has been resolved: dma-mapping: move dma_map_resource() sanity check into debug code dma_

In the Linux kernel, the following vulnerability has been resolved:

dma-mapping: move dma_map_resource() sanity check into debug code

dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
However, pfn_valid() only checks for availability of the memory map for
a PFN but it does not ensure that the PFN is actually backed by RAM. On
ARM64 with SPARSEMEM (128MB section granularity), MMIO addresses that
share a section with RAM will falsely trigger the WARN_ON_ONCE and cause
dma_map_resource() to return DMA_MAPPING_ERROR.

This causes a WARNING on Raspberry Pi 4 during spi_bcm2835 probe because
the SPI FIFO register (0xfe204004) falls in the same sparsemem section
as the end of RAM (0xf8000000-0xfbffffff), both in section 31
(0xf8000000-0xffffffff).

Move the sanity check from dma_map_resource() into debug_dma_map_phys()
and replace the unreliable pfn_valid() with pfn_valid() &&
!PageReserved(), which correctly identifies actual usable RAM without
false positives for MMIO regions that happen to have struct pages.

Since dma_map_resource() is dma_map_phys(DMA_ATTR_MMIO), the check
applies equally to both APIs. Any non-reserved page represents kernel
memory to a sufficient degree that using DMA_ATTR_MMIO on it is almost
certainly wrong and risks breaking coherency on non-coherent platforms.
ZONE_DEVICE pages used for PCI P2P DMA (MEMORY_DEVICE_PCI_P2PDMA) have
PageReserved set, so they will not trigger a false positive.

The check no longer blocks the mapping and uses err_printk() to
integrate with dma-debug filtering.