Revision faaaa53bdc6750c438887d44f99b60ad97ec74b4 authored by Jike Song on 16 December 2016, 02:51:05 UTC, committed by Zhenyu Wang on 26 December 2016, 01:45:29 UTC
gfn_to_memslot() may return NULL if the gfn is mmio or invalid. A malicious user might input a bad gfn to panic the host if we don't check it. Signed-off-by: Jike Song <jike.song@intel.com> Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
1 parent bfeca3e
percpu-rw-semaphore.txt
Percpu rw semaphores
--------------------
Percpu rw semaphores is a new read-write semaphore design that is
optimized for locking for reading.
The problem with traditional read-write semaphores is that when multiple
cores take the lock for reading, the cache line containing the semaphore
is bouncing between L1 caches of the cores, causing performance
degradation.
Locking for reading is very fast, it uses RCU and it avoids any atomic
instruction in the lock and unlock path. On the other hand, locking for
writing is very expensive, it calls synchronize_rcu() that can take
hundreds of milliseconds.
The lock is declared with "struct percpu_rw_semaphore" type.
The lock is initialized percpu_init_rwsem, it returns 0 on success and
-ENOMEM on allocation failure.
The lock must be freed with percpu_free_rwsem to avoid memory leak.
The lock is locked for read with percpu_down_read, percpu_up_read and
for write with percpu_down_write, percpu_up_write.
The idea of using RCU for optimized rw-lock was introduced by
Eric Dumazet <eric.dumazet@gmail.com>.
The code was written by Mikulas Patocka <mpatocka@redhat.com>
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