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should BIOS change the efi type when we set CONFIG_X86_RESERVE_LOW ?

RFC Xishi Qiu 1 participant 2 messages Apr 12, 2018 – Apr 23, 2018 Memory management

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Xishi Qiu

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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
...

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#1 lore raw
Quoted 10 lines · Xishi Qiu

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

Quoted 2 lines

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