On Fri, 31 May 2019 at 01:13, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> UEFI 2.8 defines an EFI_MEMORY_SP attribute bit to augment the
> interpretation of the EFI Memory Types as "reserved for a specific
> purpose". The intent of this bit is to allow the OS to identify precious
> or scarce memory resources and optionally manage it separately from
> EfiConventionalMemory. As defined older OSes that do not know about this
> attribute are permitted to ignore it and the memory will be handled
> according to the OS default policy for the given memory type.
>
> In other words, this "specific purpose" hint is deliberately weaker than
> EfiReservedMemoryType in that the system continues to operate if the OS
> takes no action on the attribute. The risk of taking no action is
> potentially unwanted / unmovable kernel allocations from the designated
> resource that prevent the full realization of the "specific purpose".
> For example, consider a system with a high-bandwidth memory pool. Older
> kernels are permitted to boot and consume that memory as conventional
> "System-RAM" newer kernels may arrange for that memory to be set aside
> by the system administrator for a dedicated high-bandwidth memory aware
> application to consume.
>
> Specifically, this mechanism allows for the elimination of scenarios
> where platform firmware tries to game OS policy by lying about ACPI SLIT
> values, i.e. claiming that a precious memory resource has a high
> distance to trigger the OS to avoid it by default.
>
> Implement simple detection of the bit for EFI memory table dumps and
> save the kernel policy for a follow-on change.
>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> drivers/firmware/efi/efi.c | 5 +++--
> include/linux/efi.h | 1 +
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 55b77c576c42..81db09485881 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -848,15 +848,16 @@ char * __init efi_md_typeattr_format(char *buf, size_t size,
> if (attr & ~(EFI_MEMORY_UC | EFI_MEMORY_WC | EFI_MEMORY_WT |
> EFI_MEMORY_WB | EFI_MEMORY_UCE | EFI_MEMORY_RO |
> EFI_MEMORY_WP | EFI_MEMORY_RP | EFI_MEMORY_XP |
> - EFI_MEMORY_NV |
> + EFI_MEMORY_NV | EFI_MEMORY_SP |
> EFI_MEMORY_RUNTIME | EFI_MEMORY_MORE_RELIABLE))
> snprintf(pos, size, "|attr=0x%016llx]",
> (unsigned long long)attr);
> else
> snprintf(pos, size,
> - "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",
> + "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]",
> attr & EFI_MEMORY_RUNTIME ? "RUN" : "",
> attr & EFI_MEMORY_MORE_RELIABLE ? "MR" : "",
> + attr & EFI_MEMORY_SP ? "SP" : "",
> attr & EFI_MEMORY_NV ? "NV" : "",
> attr & EFI_MEMORY_XP ? "XP" : "",
> attr & EFI_MEMORY_RP ? "RP" : "",
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 6ebc2098cfe1..91368f5ce114 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -112,6 +112,7 @@ typedef struct {
> #define EFI_MEMORY_MORE_RELIABLE \
> ((u64)0x0000000000010000ULL) /* higher reliability */
> #define EFI_MEMORY_RO ((u64)0x0000000000020000ULL) /* read-only */
> +#define EFI_MEMORY_SP ((u64)0x0000000000040000ULL) /* special purpose */
> #define EFI_MEMORY_RUNTIME ((u64)0x8000000000000000ULL) /* range requires runtime mapping */
> #define EFI_MEMORY_DESCRIPTOR_VERSION 1
>
>
