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Subject[tip:efi/core] efi: Reduce the amount of memblock reservations for persistent allocations
Commit-ID:  80424b02d42bb22f8ff8839cb93a84ade53b39c0
Gitweb: https://git.kernel.org/tip/80424b02d42bb22f8ff8839cb93a84ade53b39c0
Author: Ard Biesheuvel <ard.biesheuvel@linaro.org>
AuthorDate: Thu, 29 Nov 2018 18:12:29 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 30 Nov 2018 09:37:57 +0100

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 <marc.zyngier@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arend van Spriel <arend.vanspriel@broadcom.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Eric Snowberg <eric.snowberg@oracle.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jon Hunter <jonathanh@nvidia.com>
Cc: Julien Thierry <julien.thierry@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: YiFei Zhu <zhuyifei1999@gmail.com>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20181129171230.18699-11-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
drivers/firmware/efi/efi.c | 21 +++++++++++++++++----
include/linux/efi.h | 3 +++
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 */
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