[PATCH v3 03/10] efi: Enumerate EFI_MEMORY_SP

[Dan Williams]

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.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 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