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hw/i386/pc.c: CXL Fixed Memory Window should not reserve e820 in bios 

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>
This commit is contained in:
Gregory Price 2022-10-26 16:59:13 -04:00 committed by Michael S. Tsirkin
parent 15377f6e79
commit 2486dd0457
1 changed files with 0 additions and 2 deletions
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2
hw/i386/pc.c
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@ -1061,7 +1061,6 @@ void pc_memory_init(PCMachineState *pcms,
hwaddr cxl_size = MiB;
cxl_base = pc_get_cxl_range_start(pcms);
e820_add_entry(cxl_base, cxl_size, E820_RESERVED);
memory_region_init(mr, OBJECT(machine), "cxl_host_reg", cxl_size);
memory_region_add_subregion(system_memory, cxl_base, mr);
cxl_resv_end = cxl_base + cxl_size;
@ -1077,7 +1076,6 @@ void pc_memory_init(PCMachineState *pcms,
memory_region_init_io(&fw->mr, OBJECT(machine), &cfmws_ops, fw,
"cxl-fixed-memory-region", fw->size);
memory_region_add_subregion(system_memory, fw->base, &fw->mr);
e820_add_entry(fw->base, fw->size, E820_RESERVED);
cxl_fmw_base += fw->size;
cxl_resv_end = cxl_fmw_base;
}