Loading
x86/pae: use 64 bit atomic xchg function in native_ptep_get_and_clear
Using only 32-bit writes for the pte will result in an intermediate L1TF vulnerable PTE. When running as a Xen PV guest this will at once switch the guest to shadow mode resulting in a loss of performance. Use arch_atomic64_xchg() instead which will perform the requested operation atomically with all 64 bits. Some performance considerations according to: https://software.intel.com/sites/default/files/managed/ad/dc/Intel-Xeon-Scalable-Processor-throughput-latency.pdf The main number should be the latency, as there is no tight loop around native_ptep_get_and_clear(). "lock cmpxchg8b" has a latency of 20 cycles, while "lock xchg" (with a memory operand) isn't mentioned in that document. "lock xadd" (with xadd having 3 cycles less latency than xchg) has a latency of 11, so we can assume a latency of 14 for "lock xchg". Signed-off-by:Juergen Gross <jgross@suse.com> Reviewed-by: