Currently each allocation creates a new mapping. Readding the mapping as free memory (EFI_CONVENTIONAL_MEMORY) potentially allows to hand out an existing mapping, thus limiting the number of mapping descriptors in the memory map.
Mitigates a problem with current (4.8rc7) linux kernels when doing an efi_get_memory map, resulting in an infinite loop. Space for the memory map is reserved with allocate_pool (implicitly creating a new mapping) and filled. If there is insufficient slack space (8 entries) in the map, the space is freed and a new round is started, with space for one more entry. As each round increases requirement and allocation by exactly one, there is never enough slack space. (At least 32 entries are allocated, so as long as there are less than 24 entries, there is enough slack). Earlier kernels reserved no slack, and did less allocations, so this problem was not visible.
Signed-off-by: Stefan Brüns stefan.bruens@rwth-aachen.de Reviewed-by: Alexander Graf agraf@suse.de --- include/efi_loader.h | 2 +- lib/efi_loader/efi_memory.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/include/efi_loader.h b/include/efi_loader.h index 341d4a4..6d64f4b 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -117,7 +117,7 @@ void *efi_alloc(uint64_t len, int memory_type); /* More specific EFI memory allocator, called by EFI payloads */ efi_status_t efi_allocate_pages(int type, int memory_type, unsigned long pages, uint64_t *memory); -/* EFI memory free function. Not implemented today */ +/* EFI memory free function. */ efi_status_t efi_free_pages(uint64_t memory, unsigned long pages); /* EFI memory allocator for small allocations, called by EFI payloads */ efi_status_t efi_allocate_pool(int pool_type, unsigned long size, diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c index fa5c639..7051948 100644 --- a/lib/efi_loader/efi_memory.c +++ b/lib/efi_loader/efi_memory.c @@ -335,8 +335,15 @@ void *efi_alloc(uint64_t len, int memory_type)
efi_status_t efi_free_pages(uint64_t memory, unsigned long pages) { - /* We don't free, let's cross our fingers we have plenty RAM */ - return EFI_SUCCESS; + uint64_t r = 0; + + r = efi_add_memory_map(memory, pages, EFI_CONVENTIONAL_MEMORY, false); + /* Merging of adjacent free regions is missing */ + + if (r == memory) + return EFI_SUCCESS; + + return EFI_NOT_FOUND; }
efi_status_t efi_allocate_pool(int pool_type, unsigned long size,