2018-04-12 01:54:39

by Xishi Qiu

Subject: [RFC] should BIOS change the efi type when we set CONFIG_X86_RESERVE_LOW ?

Hi, I find CONFIG_X86_RESERVE_LOW=64 in my system, so trim_low_memory_range()
will reserve low 64kb memory. But efi_free_boot_services() will free it to
buddy system again later because BIOS set the type to EFI_BOOT_SERVICES_CODE.

Here is the log:
...
efi: mem03: type=3, attr=0xf, range=[0x000000000000e000-0x0000000000010000) (0MB
...

2018-04-23 10:19:52

by Xishi Qiu

Subject: Re: [RFC] should BIOS change the efi type when we set CONFIG_X86_RESERVE_LOW ?

On 2018/4/12 9:49, Xishi Qiu wrote:

> Hi, I find CONFIG_X86_RESERVE_LOW=64 in my system, so trim_low_memory_range()
> will reserve low 64kb memory. But efi_free_boot_services() will free it to
> buddy system again later because BIOS set the type to EFI_BOOT_SERVICES_CODE.
>
> Here is the log:
> ...
> efi: mem03: type=3, attr=0xf, range=[0x000000000000e000-0x0000000000010000) (0MB
> ...
>
>

When call memblock_is_region_reserved(), it will set md->num_pages = 0 if the
memblock region is reserved. But trim_low_memory_range() reserve the region
after efi, so this breaks the logic, and efi_free_boot_services() will free
the pages(efi code/data). That means trim_low_memory_range() has not reserve
the low memory range.

...
efi_reserve_boot_services()
...
trim_low_memory_range()
...
efi_free_boot_services()
...

Shall we move trim_low_memory_range() before efi_reserve_boot_services()?

Thanks,
Xishi Qiu

> .
>