| Message ID | 20221026205912.8579-1-gregory.price@memverge.com |
|---|---|
| State | New, archived |
| Headers | show |
| Series | hw/i386/pc.c: CXL Fixed Memory Window should not reserve e820 in bios | expand |
On Wed, 26 Oct 2022 16:59:13 -0400 Gregory Price <gourry.memverge@gmail.com> wrote: > 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> My understanding of e820 is limited, but from discussions with Intel folk I believe this fix to be correct - we should never have had e820 regions for CXL Fixed Memory Windows. As such Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> > --- > hw/i386/pc.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 768982ae9a..203c90fedb 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -1062,7 +1062,6 @@ 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; > @@ -1078,7 +1077,6 @@ 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; > }
diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 768982ae9a..203c90fedb 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1062,7 +1062,6 @@ 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; @@ -1078,7 +1077,6 @@ 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; }
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> --- hw/i386/pc.c | 2 -- 1 file changed, 2 deletions(-)