Commit b95a4012 authored by Uros Bizjak's avatar Uros Bizjak Committed by Joerg Roedel
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iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked_vm() 



Use atomic_long_try_cmpxchg() instead of
atomic_long_cmpxchg (*ptr, old, new) != old in incr_user_locked_vm().
cmpxchg returns success in ZF flag, so this change saves a compare
after cmpxchg (and related move instruction in front of cmpxchg).

Also, atomic_long_try_cmpxchg() implicitly assigns old *ptr
value to "old" when cmpxchg fails. There is no need to re-read
the value in the loop.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240522082729.971123-3-ubizjak@gmail.com


Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent c94ad1d5

drivers/iommu/iommufd/pages.c

+4 −3
Original line number Diff line number Diff line
@@ -809,13 +809,14 @@ static int incr_user_locked_vm(struct iopt_pages *pages, unsigned long npages) 


	lock_limit = task_rlimit(pages->source_task, RLIMIT_MEMLOCK) >>

		     PAGE_SHIFT;

	do {



	cur_pages = atomic_long_read(&pages->source_user->locked_vm);

	do {

		new_pages = cur_pages + npages;

		if (new_pages > lock_limit)

			return -ENOMEM;

	} while (atomic_long_cmpxchg(&pages->source_user->locked_vm, cur_pages,

				     new_pages) != cur_pages);

	} while (!atomic_long_try_cmpxchg(&pages->source_user->locked_vm,

					  &cur_pages, new_pages));

	return 0;

}