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>

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 16b2137d117c24af336f62ee998844075913467c..4b7cf7bc0ded9cbfd279dea2072198b38b0f3c34 100644 (file)
--- 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;