arch/arm64/kernel/proton-pack.c:953 this_cpu_set_vectors() warn: unsigned 'slot' is never less than zero.

[kernel test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   68453767131a5deec1e8f9ac92a9042f929e585d
commit: 558c303c9734af5a813739cd284879227f7297d2 arm64: Mitigate spectre style branch history side channels
date:   2 weeks ago
config: arm64-randconfig-m031-20220310 (https://download.01.org/0day-ci/archive/20220312/202203121458.ZX5wQMAu-lkp@xxxxxxxxx/config)
compiler: aarch64-linux-gcc (GCC) 11.2.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

smatch warnings:
arch/arm64/kernel/proton-pack.c:953 this_cpu_set_vectors() warn: unsigned 'slot' is never less than zero.

vim +/slot +953 arch/arm64/kernel/proton-pack.c

   948	
   949	static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
   950	{
   951		const char *v = arm64_get_bp_hardening_vector(slot);
   952	
 > 953		if (slot < 0)
   954			return;
   955	
   956		__this_cpu_write(this_cpu_vector, v);
   957	
   958		/*
   959		 * When KPTI is in use, the vectors are switched when exiting to
   960		 * user-space.
   961		 */
   962		if (arm64_kernel_unmapped_at_el0())
   963			return;
   964	
   965		write_sysreg(v, vbar_el1);
   966		isb();
   967	}
   968	

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