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Subject[RFC PATCH 1/5] efi: Detect UEFI 2.8 Special Purpose Memory
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Date
UEFI 2.8 defines an EFI_MEMORY_SP attribute bit to augment the
interpretation of the EFI Memory Types as "reserved for a special
purpose".

The proposed Linux behavior for special purpose memory is that it is
reserved for direct-access (device-dax) by default and not available for
any kernel usage, not even as an OOM fallback. Later, through udev
scripts or another init mechanism, these device-dax claimed ranges can
be reconfigured and hot-added to the available System-RAM with a unique
node identifier.

A follow-on patch integrates parsing of the ACPI HMAT to identify the
node and sub-range boundaries of EFI_MEMORY_SP designated memory. For
now, arrange for EFI_MEMORY_SP memory to be reserved.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
arch/x86/Kconfig | 18 ++++++++++++++++++
arch/x86/boot/compressed/eboot.c | 5 ++++-
arch/x86/boot/compressed/kaslr.c | 2 +-
arch/x86/include/asm/e820/types.h | 9 +++++++++
arch/x86/kernel/e820.c | 9 +++++++--
arch/x86/platform/efi/efi.c | 10 +++++++++-
include/linux/efi.h | 14 ++++++++++++++
include/linux/ioport.h | 1 +
8 files changed, 63 insertions(+), 5 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c1f9b3cf437c..cb9ca27de7a5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1961,6 +1961,24 @@ config EFI_MIXED

If unsure, say N.

+config EFI_SPECIAL_MEMORY
+ bool "EFI Special Purpose Memory Support"
+ depends on EFI
+ ---help---
+ On systems that have mixed performance classes of memory EFI
+ may indicate special purpose memory with an attribute (See
+ EFI_MEMORY_SP in UEFI 2.8). A memory range tagged with this
+ attribute may have unique performance characteristics compared
+ to the system's general purpose "System RAM" pool. On the
+ expectation that such memory has application specific usage
+ answer Y to arrange for the kernel to reserve it for
+ direct-access (device-dax) by default. The memory range can
+ later be optionally assigned to the page allocator by system
+ administrator policy. Say N to have the kernel treat this
+ memory as general purpose by default.
+
+ If unsure, say Y.
+
config SECCOMP
def_bool y
prompt "Enable seccomp to safely compute untrusted bytecode"
diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 544ac4fafd11..9b90fae21abe 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -560,7 +560,10 @@ setup_e820(struct boot_params *params, struct setup_data *e820ext, u32 e820ext_s
case EFI_BOOT_SERVICES_CODE:
case EFI_BOOT_SERVICES_DATA:
case EFI_CONVENTIONAL_MEMORY:
- e820_type = E820_TYPE_RAM;
+ if (is_efi_special(d))
+ e820_type = E820_TYPE_SPECIAL;
+ else
+ e820_type = E820_TYPE_RAM;
break;

case EFI_ACPI_MEMORY_NVS:
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 2e53c056ba20..897e46eb9714 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -757,7 +757,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
*
* Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
*/
- if (md->type != EFI_CONVENTIONAL_MEMORY)
+ if (md->type != EFI_CONVENTIONAL_MEMORY || is_efi_special(md))
continue;

if (efi_mirror_found &&
diff --git a/arch/x86/include/asm/e820/types.h b/arch/x86/include/asm/e820/types.h
index c3aa4b5e49e2..0ab8abae2e8b 100644
--- a/arch/x86/include/asm/e820/types.h
+++ b/arch/x86/include/asm/e820/types.h
@@ -28,6 +28,15 @@ enum e820_type {
*/
E820_TYPE_PRAM = 12,

+ /*
+ * Special-purpose / application-specific memory is indicated to
+ * the system via the EFI_MEMORY_SP attribute. Define an e820
+ * translation of this memory type for the purpose of
+ * reserving this range and marking it with the
+ * IORES_DESC_APPLICATION_RESERVED designation.
+ */
+ E820_TYPE_SPECIAL = 0xefffffff,
+
/*
* Reserved RAM used by the kernel itself if
* CONFIG_INTEL_TXT=y is enabled, memory of this type
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 2879e234e193..9f50dd0bbb04 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -176,6 +176,7 @@ static void __init e820_print_type(enum e820_type type)
switch (type) {
case E820_TYPE_RAM: /* Fall through: */
case E820_TYPE_RESERVED_KERN: pr_cont("usable"); break;
+ case E820_TYPE_SPECIAL: /* Fall through: */
case E820_TYPE_RESERVED: pr_cont("reserved"); break;
case E820_TYPE_ACPI: pr_cont("ACPI data"); break;
case E820_TYPE_NVS: pr_cont("ACPI NVS"); break;
@@ -1023,6 +1024,7 @@ static const char *__init e820_type_to_string(struct e820_entry *entry)
case E820_TYPE_UNUSABLE: return "Unusable memory";
case E820_TYPE_PRAM: return "Persistent Memory (legacy)";
case E820_TYPE_PMEM: return "Persistent Memory";
+ case E820_TYPE_SPECIAL: /* Fall-through: */
case E820_TYPE_RESERVED: return "Reserved";
default: return "Unknown E820 type";
}
@@ -1038,6 +1040,7 @@ static unsigned long __init e820_type_to_iomem_type(struct e820_entry *entry)
case E820_TYPE_UNUSABLE: /* Fall-through: */
case E820_TYPE_PRAM: /* Fall-through: */
case E820_TYPE_PMEM: /* Fall-through: */
+ case E820_TYPE_SPECIAL: /* Fall-through: */
case E820_TYPE_RESERVED: /* Fall-through: */
default: return IORESOURCE_MEM;
}
@@ -1050,6 +1053,7 @@ static unsigned long __init e820_type_to_iores_desc(struct e820_entry *entry)
case E820_TYPE_NVS: return IORES_DESC_ACPI_NV_STORAGE;
case E820_TYPE_PMEM: return IORES_DESC_PERSISTENT_MEMORY;
case E820_TYPE_PRAM: return IORES_DESC_PERSISTENT_MEMORY_LEGACY;
+ case E820_TYPE_SPECIAL: return IORES_DESC_APPLICATION_RESERVED;
case E820_TYPE_RESERVED_KERN: /* Fall-through: */
case E820_TYPE_RAM: /* Fall-through: */
case E820_TYPE_UNUSABLE: /* Fall-through: */
@@ -1065,13 +1069,14 @@ static bool __init do_mark_busy(enum e820_type type, struct resource *res)
return true;

/*
- * Treat persistent memory like device memory, i.e. reserve it
- * for exclusive use of a driver
+ * Treat persistent memory and other special memory ranges like
+ * device memory, i.e. reserve it for exclusive use of a driver
*/
switch (type) {
case E820_TYPE_RESERVED:
case E820_TYPE_PRAM:
case E820_TYPE_PMEM:
+ case E820_TYPE_SPECIAL:
return false;
case E820_TYPE_RESERVED_KERN:
case E820_TYPE_RAM:
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index e1cb01a22fa8..d227751f331b 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -139,7 +139,9 @@ static void __init do_add_efi_memmap(void)
case EFI_BOOT_SERVICES_CODE:
case EFI_BOOT_SERVICES_DATA:
case EFI_CONVENTIONAL_MEMORY:
- if (md->attribute & EFI_MEMORY_WB)
+ if (is_efi_special(md))
+ e820_type = E820_TYPE_SPECIAL;
+ else if (md->attribute & EFI_MEMORY_WB)
e820_type = E820_TYPE_RAM;
else
e820_type = E820_TYPE_RESERVED;
@@ -753,6 +755,12 @@ static bool should_map_region(efi_memory_desc_t *md)
if (IS_ENABLED(CONFIG_X86_32))
return false;

+ /*
+ * Special purpose memory is not mapped by default.
+ */
+ if (is_efi_special(md))
+ return false;
+
/*
* Map all of RAM so that we can access arguments in the 1:1
* mapping when making EFI runtime calls.
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 54357a258b35..cecbc2bda1da 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

@@ -128,6 +129,19 @@ typedef struct {
u64 attribute;
} efi_memory_desc_t;

+#ifdef CONFIG_EFI_SPECIAL_MEMORY
+static inline bool is_efi_special(efi_memory_desc_t *md)
+{
+ return md->type == EFI_CONVENTIONAL_MEMORY
+ && (md->attribute & EFI_MEMORY_SP);
+}
+#else
+static inline bool is_efi_special(efi_memory_desc_t *md)
+{
+ return false;
+}
+#endif
+
typedef struct {
efi_guid_t guid;
u32 headersize;
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index da0ebaec25f0..2d79841ee9b9 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -133,6 +133,7 @@ enum {
IORES_DESC_PERSISTENT_MEMORY_LEGACY = 5,
IORES_DESC_DEVICE_PRIVATE_MEMORY = 6,
IORES_DESC_DEVICE_PUBLIC_MEMORY = 7,
+ IORES_DESC_APPLICATION_RESERVED = 8,
};

/* helpers to define resources */
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