[PULL,v3,63/81] hw/i386/pc.c: CXL Fixed Memory Window should not reserve e820 in bios

Commit Message

Michael S. Tsirkin Nov. 5, 2022, 5:18 p.m. UTC

From: Gregory Price <[e-mail]>

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 <[e-mail]>
Message-Id: <[e-mail]>
Reviewed-by: Michael S. Tsirkin <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Acked-by: Jonathan Cameron <[e-mail]>
---
 hw/i386/pc.c | 2 --
 1 file changed, 2 deletions(-)

Patch

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index ef14da5094..546b703cb4 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -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;
             }