efi/memreserve: deal with memreserve entries in unmapped memory

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>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 16b2137d117c..4b7cf7bc0ded 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -1009,14 +1009,16 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
 
         /* 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);
                 index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
                 if (index < rsv->size) {
                         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 */
@@ -1024,7 +1026,13 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
         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;