efi: Reduce the amount of memblock reservations for persistent allocations

The current implementation of efi_mem_reserve_persistent() is rather
naive, in the sense that for each invocation, it creates a separate
linked list entry to describe the reservation. Since the linked list
entries themselves need to persist across subsequent kexec reboots,
every reservation created this way results in two memblock_reserve()
calls at the next boot.

On arm64 systems with 100s of CPUs, this may result in a excessive
number of memblock reservations, and needless fragmentation.

So instead, make use of the newly updated struct linux_efi_memreserve
layout to put multiple reservations into a single linked list entry.
This should get rid of the numerous tiny memblock reservations, and
effectively cut the total number of reservations in half on arm64
systems with many CPUs.

 [ mingo: build warning fix. ]

Tested-by: Marc Zyngier <[email protected]>
Signed-off-by: Ard Biesheuvel <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arend van Spriel <[email protected]>
Cc: Bhupesh Sharma <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Eric Snowberg <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Jon Hunter <[email protected]>
Cc: Julien Thierry <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matt Fleming <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sai Praneeth Prakhya <[email protected]>
Cc: Sedat Dilek <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: YiFei Zhu <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

2 files changed, 20 insertions, 4 deletions

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 80b11521627a..4c46ff6f2242 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -997,8 +997,8 @@ static int __init efi_memreserve_map_root(void)
 int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
 {
 	struct linux_efi_memreserve *rsv;
-	int rsvsize = EFI_MEMRESERVE_SIZE(1);
-	int rc;
+	unsigned long prsv;
+	int rc, index;
 
 	if (efi_memreserve_root == (void *)ULONG_MAX)
 		return -ENODEV;
@@ -1009,11 +1009,24 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
 			return rc;
 	}
 
-	rsv = kmalloc(rsvsize, GFP_ATOMIC);
+	/* 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);
+		index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
+		if (index < rsv->size) {
+			rsv->entry[index].base = addr;
+			rsv->entry[index].size = size;
+
+			return 0;
+		}
+	}
+
+	/* no slot found - allocate a new linked list entry */
+	rsv = (struct linux_efi_memreserve *)__get_free_page(GFP_ATOMIC);
 	if (!rsv)
 		return -ENOMEM;
 
-	rsv->size = 1;
+	rsv->size = EFI_MEMRESERVE_COUNT(PAGE_SIZE);
 	atomic_set(&rsv->count, 1);
 	rsv->entry[0].base = addr;
 	rsv->entry[0].size = size;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 4f27640fdcdc..becd5d76a207 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1724,4 +1724,7 @@ struct linux_efi_memreserve {
 #define EFI_MEMRESERVE_SIZE(count) (sizeof(struct linux_efi_memreserve) + \
 	(count) * sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
 
+#define EFI_MEMRESERVE_COUNT(size) (((size) - sizeof(struct linux_efi_memreserve)) \
+	/ sizeof(((struct linux_efi_memreserve *)0)->entry[0]))
+
 #endif /* _LINUX_EFI_H */