On Wed, May 18, 2022 at 01:18:40PM +0530, Vivek Kumar wrote:

Add check for pte_valid in saveable page after being checked for
the rest. This is required as PTE is removed for pages allocated
with dma_alloc_coherent with DMA_ATTR_NO_KERNEL_MAPPING flag set.
This patch makes sure that these pages are not considered for
snapshot.

I don't think we ever remove kernel PTEs for DMA_ATTR_NO_KERNEL_MAPPING.
If the allocation did come from highmem they never had one to start
with.  The logic here looks a bit fishy to me.