x86: Use rd/wr fs/gs base in arch_prctl
Convert arch_prctl to use the new instructions to
change fs/gs if available, instead of using MSRs.
This is merely a small performance optimization,
no new functionality.
With the new instructions the syscall is really obsolete,
as everything can be set directly in ring 3. But the syscall
is widely used by existing software, so we still support it.
The syscall still enforces that the addresses are not
in kernel space, even though that is not needed more.
This is mainly so that the programs written for new CPUs
do not suddenly fail on old CPUs.
With the new instructions available it prefers to use
them in the context switch, instead of using the old
"use GDT segment rewrite" trick.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
1 file changed
