3 files changed, 48 insertions, 0 deletions

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index b248870a9806..bcc378c19ebe 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -75,6 +75,27 @@ config EFI_MAX_FAKE_MEM
 	  Ranges can be set up to this value using comma-separated list.
 	  The default value is 8.
 
+config EFI_SOFT_RESERVE
+	bool "Reserve EFI Specific Purpose Memory"
+	depends on EFI && EFI_STUB && ACPI_HMAT
+	default ACPI_HMAT
+	help
+	  On systems that have mixed performance classes of memory EFI
+	  may indicate specific 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,
+	  and its base EFI memory type is "conventional" answer Y to
+	  arrange for the kernel to reserve it as a "Soft Reserved"
+	  resource, and set aside for direct-access (device-dax) by
+	  default. The memory range can later be optionally assigned to
+	  the page allocator by system administrator policy via the
+	  device-dax kmem facility. Say N to have the kernel treat this
+	  memory as "System RAM" by default.
+
+	  If unsure, say Y.
+
 config EFI_PARAMS_FROM_FDT
 	bool
 	help
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index f8f8e273d809..e1cb915b45c6 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -81,6 +81,11 @@ bool efi_runtime_disabled(void)
 	return disable_runtime;
 }
 
+bool __pure __efi_soft_reserve_enabled(void)
+{
+	return !efi_enabled(EFI_MEM_NO_SOFT_RESERVE);
+}
+
 static int __init parse_efi_cmdline(char *str)
 {
 	if (!str) {
@@ -94,6 +99,9 @@ static int __init parse_efi_cmdline(char *str)
 	if (parse_option_str(str, "noruntime"))
 		disable_runtime = true;
 
+	if (parse_option_str(str, "nosoftreserve"))
+		set_bit(EFI_MEM_NO_SOFT_RESERVE, &efi.flags);
+
 	return 0;
 }
 early_param("efi", parse_efi_cmdline);
diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 35dbc2791c97..e02579907f2e 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -32,6 +32,7 @@ static unsigned long __chunk_size = EFI_READ_CHUNK_SIZE;
 static int __section(.data) __nokaslr;
 static int __section(.data) __quiet;
 static int __section(.data) __novamap;
+static bool __section(.data) efi_nosoftreserve;
 
 int __pure nokaslr(void)
 {
@@ -45,6 +46,10 @@ int __pure novamap(void)
 {
 	return __novamap;
 }
+bool __pure __efi_soft_reserve_enabled(void)
+{
+	return !efi_nosoftreserve;
+}
 
 #define EFI_MMAP_NR_SLACK_SLOTS	8
 
@@ -211,6 +216,10 @@ again:
 		if (desc->type != EFI_CONVENTIONAL_MEMORY)
 			continue;
 
+		if (efi_soft_reserve_enabled() &&
+		    (desc->attribute & EFI_MEMORY_SP))
+			continue;
+
 		if (desc->num_pages < nr_pages)
 			continue;
 
@@ -305,6 +314,10 @@ efi_status_t efi_low_alloc_above(efi_system_table_t *sys_table_arg,
 		if (desc->type != EFI_CONVENTIONAL_MEMORY)
 			continue;
 
+		if (efi_soft_reserve_enabled() &&
+		    (desc->attribute & EFI_MEMORY_SP))
+			continue;
+
 		if (desc->num_pages < nr_pages)
 			continue;
 
@@ -484,6 +497,12 @@ efi_status_t efi_parse_options(char const *cmdline)
 			__novamap = 1;
 		}
 
+		if (IS_ENABLED(CONFIG_EFI_SOFT_RESERVE) &&
+		    !strncmp(str, "nosoftreserve", 7)) {
+			str += strlen("nosoftreserve");
+			efi_nosoftreserve = 1;
+		}
+
 		/* Group words together, delimited by "," */
 		while (*str && *str != ' ' && *str != ',')
 			str++;