x86/fpu: Get rid of the FNSAVE optimization
mainline inclusion from mainline-v5.14-rc1 commit 08ded2cd category: feature bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I590ZC CVE: NA Intel-SIG: commit 08ded2cd x86/fpu: Get rid of the FNSAVE optimization. -------------------------------- The FNSAVE support requires conditionals in quite some call paths because FNSAVE reinitializes the FPU hardware. If the save has to preserve the FPU register state then the caller has to conditionally restore it from memory when FNSAVE is in use. This also requires a conditional in context switch because the restore avoidance optimization cannot work with FNSAVE. As this only affects 20+ years old CPUs there is really no reason to keep this optimization effective for FNSAVE. It's about time to not optimize for antiques anymore. Just unconditionally FRSTOR the save content to the registers and clean up the conditionals all over the place. Suggested-by: NDave Hansen <dave.hansen@linux.intel.com> Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NBorislav Petkov <bp@suse.de> Reviewed-by: NBorislav Petkov <bp@suse.de> Link: https://lkml.kernel.org/r/20210623121454.617369268@linutronix.deSigned-off-by: NLin Wang <lin.x.wang@intel.com> Signed-off-by: NAichun Shi <aichun.shi@intel.com>
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