[RFC PATCH 1/4] efi/libstub: Decouple memory bitmap from the unaccepted table

["Pratik R. Sampat" <prsampat@amd.com>]

Memory hotplug in secure environments requires the unaccepted memory
bitmap to grow as new memory is added. Currently, the bitmap is
implemented as a flexible array member at the end of struct
efi_unaccepted_memory, which is reserved by memblock at boot and cannot
be resized without reallocating the entire structure.

Replace the flexible array member with a pointer. This allows the bitmap
to be allocated and managed independently from the unaccepted memory
table, enabling dynamic growth to support memory hotplug.

Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
---
 arch/x86/boot/compressed/efi.h                |  2 +-
 arch/x86/include/asm/unaccepted_memory.h      |  9 +++++++++
 .../firmware/efi/libstub/unaccepted_memory.c  | 11 ++++++++++-
 drivers/firmware/efi/unaccepted_memory.c      | 19 ++++++++++++++-----
 include/linux/efi.h                           |  2 +-
 5 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/arch/x86/boot/compressed/efi.h b/arch/x86/boot/compressed/efi.h
index b22300970f97..4f7027f33def 100644
--- a/arch/x86/boot/compressed/efi.h
+++ b/arch/x86/boot/compressed/efi.h
@@ -102,7 +102,7 @@ struct efi_unaccepted_memory {
 	u32 unit_size;
 	u64 phys_base;
 	u64 size;
-	unsigned long bitmap[];
+	unsigned long *bitmap;
 };
 
 static inline int efi_guidcmp (efi_guid_t left, efi_guid_t right)
diff --git a/arch/x86/include/asm/unaccepted_memory.h b/arch/x86/include/asm/unaccepted_memory.h
index f5937e9866ac..5da80e68d718 100644
--- a/arch/x86/include/asm/unaccepted_memory.h
+++ b/arch/x86/include/asm/unaccepted_memory.h
@@ -24,4 +24,13 @@ static inline struct efi_unaccepted_memory *efi_get_unaccepted_table(void)
 		return NULL;
 	return __va(efi.unaccepted);
 }
+
+static inline unsigned long *efi_get_unaccepted_bitmap(void)
+{
+	struct efi_unaccepted_memory *unaccepted = efi_get_unaccepted_table();
+
+	if (!unaccepted)
+		return NULL;
+	return __va(unaccepted->bitmap);
+}
 #endif
diff --git a/drivers/firmware/efi/libstub/unaccepted_memory.c b/drivers/firmware/efi/libstub/unaccepted_memory.c
index 757dbe734a47..c1370fc14555 100644
--- a/drivers/firmware/efi/libstub/unaccepted_memory.c
+++ b/drivers/firmware/efi/libstub/unaccepted_memory.c
@@ -63,13 +63,22 @@ efi_status_t allocate_unaccepted_bitmap(__u32 nr_desc,
 				   EFI_UNACCEPTED_UNIT_SIZE * BITS_PER_BYTE);
 
 	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
-			     sizeof(*unaccepted_table) + bitmap_size,
+			     sizeof(*unaccepted_table),
 			     (void **)&unaccepted_table);
 	if (status != EFI_SUCCESS) {
 		efi_err("Failed to allocate unaccepted memory config table\n");
 		return status;
 	}
 
+	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
+			     bitmap_size,
+			     (void **)&unaccepted_table->bitmap);
+	if (status != EFI_SUCCESS) {
+		efi_bs_call(free_pool, unaccepted_table);
+		efi_err("Failed to allocate unaccepted memory bitmap\n");
+		return status;
+	}
+
 	unaccepted_table->version = 1;
 	unaccepted_table->unit_size = EFI_UNACCEPTED_UNIT_SIZE;
 	unaccepted_table->phys_base = unaccepted_start;
diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
index c2c067eff634..4479aad258f8 100644
--- a/drivers/firmware/efi/unaccepted_memory.c
+++ b/drivers/firmware/efi/unaccepted_memory.c
@@ -36,7 +36,7 @@ void accept_memory(phys_addr_t start, unsigned long size)
 	unsigned long range_start, range_end;
 	struct accept_range range, *entry;
 	phys_addr_t end = start + size;
-	unsigned long flags;
+	unsigned long flags, *bitmap;
 	u64 unit_size;
 
 	unaccepted = efi_get_unaccepted_table();
@@ -124,8 +124,12 @@ void accept_memory(phys_addr_t start, unsigned long size)
 	list_add(&range.list, &accepting_list);
 
 	range_start = range.start;
-	for_each_set_bitrange_from(range_start, range_end, unaccepted->bitmap,
-				   range.end) {
+
+	bitmap = efi_get_unaccepted_bitmap();
+	if (!bitmap)
+		return;
+
+	for_each_set_bitrange_from(range_start, range_end, bitmap, range.end) {
 		unsigned long phys_start, phys_end;
 		unsigned long len = range_end - range_start;
 
@@ -147,7 +151,7 @@ void accept_memory(phys_addr_t start, unsigned long size)
 		arch_accept_memory(phys_start, phys_end);
 
 		spin_lock(&unaccepted_memory_lock);
-		bitmap_clear(unaccepted->bitmap, range_start, len);
+		bitmap_clear(bitmap, range_start, len);
 	}
 
 	list_del(&range.list);
@@ -197,7 +201,12 @@ bool range_contains_unaccepted_memory(phys_addr_t start, unsigned long size)
 
 	spin_lock_irqsave(&unaccepted_memory_lock, flags);
 	while (start < end) {
-		if (test_bit(start / unit_size, unaccepted->bitmap)) {
+		unsigned long *bitmap = efi_get_unaccepted_bitmap();
+
+		if (!bitmap)
+			break;
+
+		if (test_bit(start / unit_size, bitmap)) {
 			ret = true;
 			break;
 		}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a98cc39e7aaa..a74b393c54d8 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -545,7 +545,7 @@ struct efi_unaccepted_memory {
 	u32 unit_size;
 	u64 phys_base;
 	u64 size;
-	unsigned long bitmap[];
+	unsigned long *bitmap;
 };
 
 /*
-- 
2.51.1