On 10/01/2025 14:31, Usama Arif wrote: > > > On 10/01/2025 07:32, Ard Biesheuvel wrote: >> On Thu, 9 Jan 2025 at 17:32, Usama Arif <usamaarif642@xxxxxxxxx> wrote: >>> >>> >>> >>> On 09/01/2025 16:15, Ard Biesheuvel wrote: > >>> I think in the end whoevers' responsibility it is, the easiest path forward >>> seems to be in kernel? (and not firmware or libstub) >>> >> >> Agreed. But as I pointed out in the other thread, the memory >> attributes table only augments the memory map with permission >> information, and can be disregarded, and given how badly we mangle the >> memory map on x86, maybe this is the right choice here. >> >>>> >>>>> The next ideal place would be in libstub. However, it looks like >>>>> InstallMemoryAttributesTable [2] is not available as a boot service >>>>> call option [3], [4], and install_configuration_table does not >>>>> seem to work as a valid substitute. >>>>> >>>> >>>> To do what, exactly? >>>> >>> >>> To change the memory type from System RAM to either reserved or >>> something more appropriate, i.e. any type that is not touched by >>> kexec or any other userspace. >>> >>> Basically the example code I attached at the end of the cover letter in >>> https://lore.kernel.org/all/20250108215957.3437660-1-usamaarif642@xxxxxxxxx/ >>> It could be EFI_ACPI_RECLAIM_MEMORY or EFI_RESERVED_TYPE, both of which aren't >>> touched by kexec. >>> >> >> This is a kexec problem (on x86 only) so let's fix it there. > > > I don't believe we can accurately tell if we are booting from a cold boot or kexec. > There is bootloader_type available for x86, but not sure if we should rely on > that. I think a way forward would be to move it behind a Kconfig option, something like > below, which defaults to n for x86. Anyone who needs it can enable it. What do you think? > Or we can do something like below? diff --git a/drivers/firmware/efi/memattr.c b/drivers/firmware/efi/memattr.c index d131781e2d7b..4add694b18d0 100644 --- a/drivers/firmware/efi/memattr.c +++ b/drivers/firmware/efi/memattr.c @@ -24,6 +24,15 @@ int __init efi_memattr_init(void) efi_memory_attributes_table_t *tbl; unsigned long size; +#ifdef CONFIG_X86_64 + /* + * On x86_64, do not initialize memory attributes table + * if booting from kexec + */ + if (bootloader_type >> 4 == 0xd) + return 0; +#endif + if (efi_mem_attr_table == EFI_INVALID_TABLE_ADDR) return 0;
