Early-boot e820 records will be inserted by the bios/efi/early boot
software and be reported to the kernel via insert_resource. Later, when
CXL drivers iterate through the regions again, they will insert another
resource and make the RESERVED memory area a child.
This RESERVED memory area causes the memory region to become unusable,
and as a result attempting to create memory regions with
`cxl create-region ...`
Will fail due to the RESERVED area intersecting with the CXL window.
During boot the following traceback is observed:
0xffffffff81101650 in insert_resource_expand_to_fit ()
0xffffffff83d964c5 in e820__reserve_resources_late ()
0xffffffff83e03210 in pcibios_resource_survey ()
0xffffffff83e04f4a in pcibios_init ()
Which produces a call to reserve the CFMWS area:
(gdb) p *new
$54 = {start = 0x290000000, end = 0x2cfffffff, name = "Reserved",
flags = 0x200, desc = 0x7, parent = 0x0, sibling = 0x0,
child = 0x0}
Later the Kernel parses ACPI tables and reserves the exact same area as
the CXL Fixed Memory Window:
0xffffffff811016a4 in insert_resource_conflict ()
insert_resource ()
0xffffffff81a81389 in cxl_parse_cfmws ()
0xffffffff818c4a81 in call_handler ()
acpi_parse_entries_array ()
(gdb) p/x *new
$59 = {start = 0x290000000, end = 0x2cfffffff, name = "CXL Window 0",
flags = 0x200, desc = 0x0, parent = 0x0, sibling = 0x0,
child = 0x0}
This produces the following output in /proc/iomem:
590000000-68fffffff : CXL Window 0
590000000-68fffffff : Reserved
This reserved area causes `get_free_mem_region()` to fail due to a check
against `__region_intersects()`. Due to this reserved area, the
intersect check will only ever return REGION_INTERSECTS, which causes
`cxl create-region` to always fail.
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Message-Id: <20221026205912.8579-1-gregory.price@memverge.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
2486dd0457