target-i386: add RDTSCP support
RDTSCP reads the time stamp counter and atomically also the content of a 32-bit MSR, which can be freely set by the OS. This allows CPU local data to be queried by userspace. Linux uses this to allow a fast implementation of the getcpu() syscall, which uses the vsyscall page to avoid a context switch. AMD CPUs since K8RevF and Intel CPUs since Nehalem support this instruction. RDTSCP is guarded by the RDTSCP CPUID bit (Fn8000_0001:EDX[27]). Signed-off-by: NAndre Przywara <andre.przywara@amd.com> Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
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