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Let's test some basic functionality using /dev/mem. These tests will implicitly cover some PAT (Page Attribute Handling) handling on x86. These tests will only run when /dev/mem access to the first two pages in physical address space is possible and allowed; otherwise, the tests are skipped. On current x86-64 with PAT inside a VM, all tests pass: TAP version 13 1..6 # Starting 6 tests from 1 test cases. # RUN pfnmap.madvise_disallowed ... # OK pfnmap.madvise_disallowed ok 1 pfnmap.madvise_disallowed # RUN pfnmap.munmap_split ... # OK pfnmap.munmap_split ok 2 pfnmap.munmap_split # RUN pfnmap.mremap_fixed ... # OK pfnmap.mremap_fixed ok 3 pfnmap.mremap_fixed # RUN pfnmap.mremap_shrink ... # OK pfnmap.mremap_shrink ok 4 pfnmap.mremap_shrink # RUN pfnmap.mremap_expand ... # OK pfnmap.mremap_expand ok 5 pfnmap.mremap_expand # RUN pfnmap.fork ... # OK pfnmap.fork ok 6 pfnmap.fork # PASSED: 6 / 6 tests passed. # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0 However, we are able to trigger: [ 27.888251] x86/PAT: pfnmap:1790 freeing invalid memtype [mem 0x00000000-0x00000fff] There are probably more things worth testing in the future, such as MAP_PRIVATE handling. But this set of tests is sufficient to cover most of the things we will rework regarding PAT handling. Link: https://lkml.kernel.org/r/20250509153033.952746-1-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: Dev Jain <dev.jain@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>