[U-Boot] [PATCH v3] efi_loader: Reserve unaccessible memory

[Alexander Graf <agraf@suse.de>]

On some systems, not all RAM may be usable within U-Boot. Maybe the
memory maps are incomplete, maybe it's used as workaround for broken
DMA. But whatever the reason may be, a platform can say that it does
not wish to have its RAM accessed above a certain address by defining
board_get_usable_ram_top().

In the efi_loader world, we ignored that hint, mostly because very few
boards actually have real restrictions around this.

So let's honor the board's wish to not access high addresses during
boot time. The best way to do so is by indicating the respective pages
as "allocated by firmware". That way, Operating Systems will still
use the pages after boot, but before boot no allocation will use them.

Reported-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>

---

v1 -> v2:

  - Reserve banks that start above ram_top
  - Improve inline comments
  - Fix 32bit target with ram_top = 0 (>=4G)

v2 -> v3:

  - Fix 32bit target with ram_top = 0 for real (map to 1<<32
    rather than 1<<32-1)
---
 include/common.h            | 11 +++++++++++
 lib/efi_loader/efi_memory.c | 32 +++++++++++++++++++++++++++++---
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/common.h b/include/common.h
index 3f69943887..8f295c2f30 100644
--- a/include/common.h
+++ b/include/common.h
@@ -106,6 +106,17 @@ int mdm_init(void);
 void board_show_dram(phys_size_t size);
 
 /**
+ * Get the uppermost pointer that is valid to access
+ *
+ * Some systems may not map all of their address space. This function allows
+ * boards to indicate what their highest support pointer value is for DRAM
+ * access.
+ *
+ * @param total_size	Size of U-Boot (unused?)
+ */
+ulong board_get_usable_ram_top(ulong total_size);
+
+/**
  * arch_fixup_fdt() - Write arch-specific information to fdt
  *
  * Defined in arch/$(ARCH)/lib/bootm-fdt.c
diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
index f225a9028c..73bfbb65c4 100644
--- a/lib/efi_loader/efi_memory.c
+++ b/lib/efi_loader/efi_memory.c
@@ -551,8 +551,13 @@ efi_status_t efi_get_memory_map(efi_uintn_t *memory_map_size,
 
 __weak void efi_add_known_memory(void)
 {
+	u64 ram_top = board_get_usable_ram_top(0) & ~EFI_PAGE_MASK;
 	int i;
 
+	/* Fix for 32bit targets with ram_top@4G */
+	if (!ram_top)
+		ram_top = 0x100000000ULL;
+
 	/* Add RAM */
 	for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
 		u64 ram_end, ram_start, pages;
@@ -564,11 +569,32 @@ __weak void efi_add_known_memory(void)
 		ram_end &= ~EFI_PAGE_MASK;
 		ram_start = (ram_start + EFI_PAGE_MASK) & ~EFI_PAGE_MASK;
 
-		if (ram_end > ram_start) {
-			pages = (ram_end - ram_start) >> EFI_PAGE_SHIFT;
+		if (ram_end <= ram_start) {
+			/* Invalid mapping, keep going. */
+			continue;
+		}
+
+		pages = (ram_end - ram_start) >> EFI_PAGE_SHIFT;
 
+		efi_add_memory_map(ram_start, pages,
+				   EFI_CONVENTIONAL_MEMORY, false);
+
+		/*
+		 * Boards may indicate to the U-Boot memory core that they
+		 * can not support memory above ram_top. Let's honor this
+		 * in the efi_loader subsystem too by declaring any memory
+		 * above ram_top as "already occupied by firmware".
+		 */
+		if (ram_top < ram_start) {
+			/* ram_top is before this region, reserve all */
 			efi_add_memory_map(ram_start, pages,
-					   EFI_CONVENTIONAL_MEMORY, false);
+					   EFI_BOOT_SERVICES_DATA, true);
+		} else if ((ram_top >= ram_start) && (ram_top < ram_end)) {
+			/* ram_top is inside this region, reserve parts */
+			pages = (ram_end - ram_top) >> EFI_PAGE_SHIFT;
+
+			efi_add_memory_map(ram_top, pages,
+					   EFI_BOOT_SERVICES_DATA, true);
 		}
 	}
 }
-- 
2.12.3