[PATCH 2/2] efi: efi_mem_reserve(): don't reserve through memblock after mm_init()

[Nicolai Stange]

Before invoking the arch specific handler, efi_mem_reserve() reserves
the given memory region through memblock.

efi_mem_reserve() can get called after mm_init() though -- through
efi_bgrt_init(), for example. After mm_init(), memblock is dead and should
not be used anymore.

Let efi_mem_reserve() check whether memblock is dead and not do the
reservation if so. Emit a warning from the generic efi_arch mem_reserve()
in this case: if the architecture doesn't provide any other means of
registering the region as reserved, the operation would be a nop.

Fixes: 4bc9f92e64c8 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
---
 drivers/firmware/efi/efi.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 92914801e388..12b2e3a6d73f 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -403,7 +403,10 @@ u64 __init efi_mem_desc_end(efi_memory_desc_t *md)
 	return end;
 }
 
-void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size) {}
+void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size)
+{
+	WARN(slab_is_available(), "efi_mem_reserve() has no effect");
+}
 
 /**
  * efi_mem_reserve - Reserve an EFI memory region
@@ -419,7 +422,7 @@ void __init __weak efi_arch_mem_reserve(phys_addr_t addr, u64 size) {}
  */
 void __init efi_mem_reserve(phys_addr_t addr, u64 size)
 {
-	if (!memblock_is_region_reserved(addr, size))
+	if (slab_is_available() && !memblock_is_region_reserved(addr, size))
 		memblock_reserve(addr, size);
 
 	/*
-- 
2.11.0