From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Sun, 9 Jun 2019 20:17:44 +0200
Subject: efi/memreserve: deal with memreserve entries in unmapped memory
Git-commit: 18df7577adae6c6c778bf774b3aebcacbc1fb439
Patch-mainline: v5.2-rc7
References: bsc#1174685

Ensure that the EFI memreserve entries can be accessed, even if they
are located in memory that the kernel (e.g., a crashkernel) omits from
the linear map.

Fixes: 80424b02d42b ("efi: Reduce the amount of memblock reservations ...")
Cc: <stable@vger.kernel.org> # 5.0+
Reported-by: Jonathan Richardson <jonathan.richardson@broadcom.com>
Reviewed-by: Jonathan Richardson <jonathan.richardson@broadcom.com>
Tested-by: Jonathan Richardson <jonathan.richardson@broadcom.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[mb: add include of sizes.h to fix compilation error]
Signed-off-by: Matthias Brugger <mbrugger@suse.com>
---
 drivers/firmware/efi/efi.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -32,6 +32,8 @@
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
 
+#include <linux/sizes.h>
+
 #include <asm/early_ioremap.h>
 
 struct efi __read_mostly efi = {
@@ -958,7 +960,7 @@ int __ref efi_mem_reserve_persistent(phy
 
 	/* first try to find a slot in an existing linked list entry */
 	for (prsv = efi_memreserve_root->next; prsv; prsv = rsv->next) {
-		rsv = __va(prsv);
+		rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
 		/* implement atomic_fetch_add_unless for
 		 * index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
 		 */
@@ -973,8 +975,10 @@ int __ref efi_mem_reserve_persistent(phy
 			rsv->entry[index].base = addr;
 			rsv->entry[index].size = size;
 
+			memunmap(rsv);
 			return 0;
 		}
+		memunmap(rsv);
 	}
 
 	/* no slot found - allocate a new linked list entry */
@@ -982,7 +986,13 @@ int __ref efi_mem_reserve_persistent(phy
 	if (!rsv)
 		return -ENOMEM;
 
-	rsv->size = EFI_MEMRESERVE_COUNT(PAGE_SIZE);
+	/*
+	 * The memremap() call above assumes that a linux_efi_memreserve entry
+	 * never crosses a page boundary, so let's ensure that this remains true
+	 * even when kexec'ing a 4k pages kernel from a >4k pages kernel, by
+	 * using SZ_4K explicitly in the size calculation below.
+	 */
+	rsv->size = EFI_MEMRESERVE_COUNT(SZ_4K);
 	atomic_set(&rsv->count, 1);
 	rsv->entry[0].base = addr;
 	rsv->entry[0].size = size;