On Mon, Jun 05, 2017 at 08:04:35AM +0000, Ard Biesheuvel wrote:
> On ARM, regions of memory that are described by UEFI as having special
> significance to the firmware itself are omitted from the linear mapping.
> This is necessary since we cannot guarantee that alternate mappings of
> the same physical region will use attributes that are compatible with
> the ones we use for the linear mapping, and aliases with mismatched
> attributes are prohibited by the architecture.
>
> The above does not apply to ACPI reclaim regions: such regions have no
> special significance to the firmware, and it is up to the OS to decide
> whether or not to preserve them after it has consumed their contents,
> and for how long, after which time the OS can use the memory in any way
> it likes. In the Linux case, such regions are preserved indefinitely,
> and are simply treated the same way as other 'reserved' memory types.
>
> Punching holes into the linear mapping causes page table fragmentation,
> which increases TLB pressure, and so we should avoid doing so if we can.
> So add a special case for regions of type EFI_ACPI_RECLAIM_MEMORY, and
> memblock_reserve() them instead of marking them MEMBLOCK_NOMAP.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Sounds sane to me. FWIW:
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Thanks,
Mark.
> ---
> drivers/firmware/efi/arm-init.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
> index 1027d7b44358..0aa4ce7b4fbb 100644
> --- a/drivers/firmware/efi/arm-init.c
> +++ b/drivers/firmware/efi/arm-init.c
> @@ -159,6 +159,7 @@ static __init int is_usable_memory(efi_memory_desc_t *md)
> switch (md->type) {
> case EFI_LOADER_CODE:
> case EFI_LOADER_DATA:
> + case EFI_ACPI_RECLAIM_MEMORY:
> case EFI_BOOT_SERVICES_CODE:
> case EFI_BOOT_SERVICES_DATA:
> case EFI_CONVENTIONAL_MEMORY:
> @@ -211,6 +212,10 @@ static __init void reserve_regions(void)
>
> if (!is_usable_memory(md))
> memblock_mark_nomap(paddr, size);
> +
> + /* keep ACPI reclaim memory intact for kexec etc. */
> + if (md->type == EFI_ACPI_RECLAIM_MEMORY)
> + memblock_reserve(paddr, size);
> }
> }
> }
> --
> 2.9.3
>
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