[PATCH 1/2] firmware/efi: Tell memblock about EFI reservations

[Marc Zyngier]

kexec_load_file() relies on the memblock infrastructure to avoid
stamping over regions of memory that are essential to the survival
of the system.

However, nobody seems to agree how to flag these regions as reserved,
and (for example) EFI only publishes its reservations in /proc/iomem
for the benefit of the traditional, userspace based kexec tool.

On arm64 platforms with GICv3, this can result in the payload being
placed at the location of the LPI tables. Shock, horror!

Let's augment the EFI reservation code with a memblock_reserve() call,
protecting our dear tables from the secondary kernel invasion.

At some point, someone will have to go and figure out a way to unify
these multiple reservation trees, because sprinkling random reservation
calls is only a temporary workaround.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 drivers/firmware/efi/efi.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 4b7ee3fa9224..026b02f5f7d8 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -896,11 +896,25 @@ static int __init efi_memreserve_map_root(void)
 static int efi_mem_reserve_iomem(phys_addr_t addr, u64 size)
 {
 	struct resource *res, *parent;
+	int ret;
 
 	res = kzalloc(sizeof(struct resource), GFP_ATOMIC);
 	if (!res)
 		return -ENOMEM;
 
+	/*
+	 * Given that efi_mem_reserve_iomem() can be called at any
+	 * time, only call memblock_reserve() if the architecture
+	 * keeps the infrastructure around.
+	 */
+	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
+		ret = memblock_reserve(addr, size);
+		if (ret) {
+			kfree(res);
+			return ret;
+		}
+	}
+
 	res->name	= "reserved";
 	res->flags	= IORESOURCE_MEM;
 	res->start	= addr;
@@ -908,7 +922,14 @@ static int efi_mem_reserve_iomem(phys_addr_t addr, u64 size)
 
 	/* we expect a conflict with a 'System RAM' region */
 	parent = request_resource_conflict(&iomem_resource, res);
-	return parent ? request_resource(parent, res) : 0;
+	ret = parent ? request_resource(parent, res) : 0;
+	if (ret) {
+		kfree(res);
+		if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
+			memblock_free(addr, size);
+	}
+
+	return ret;
 }
 
 int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
-- 
2.29.2