Re: [PATCH v1 2/4] x86/process: Add a debug interface to change LAM tag width

[Maciej Wieczor-Retman]

I'll correct these in the next version.

On 2026-02-21 at 00:41:41 +0800, kernel test robot wrote:
>Hi Maciej,
>
>kernel test robot noticed the following build warnings:
>
>[auto build test WARNING on tip/x86/core]
>[also build test WARNING on peterz-queue/sched/core akpm-mm/mm-everything linus/master v6.19 next-20260220]
>[If your patch is applied to the wrong git tree, kindly drop us a note.
>And when submitting patch, we suggest to use '--base' as documented in
>https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
>url:    https://github.com/intel-lab-lkp/linux/commits/Maciej-Wieczor-Retman/x86-process-Shorten-the-default-LAM-tag-width/20260220-205155
>base:   tip/x86/core
>patch link:    https://lore.kernel.org/r/5ed38af72848015f3417c462e624e52891dc14ed.1771589807.git.m.wieczorretman%40pm.me
>patch subject: [PATCH v1 2/4] x86/process: Add a debug interface to change LAM tag width
>config: x86_64-buildonly-randconfig-001-20260220 (https://download.01.org/0day-ci/archive/20260221/202602210040.C4PVoS0u-lkp@xxxxxxxxx/config)
>compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
>rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
>reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260221/202602210040.C4PVoS0u-lkp@xxxxxxxxx/reproduce)
>
>If you fix the issue in a separate patch/commit (i.e. not just a new version of
>the same patch/commit), kindly add following tags
>| Reported-by: kernel test robot <lkp@xxxxxxxxx>
>| Closes: https://lore.kernel.org/oe-kbuild-all/202602210040.C4PVoS0u-lkp@xxxxxxxxx/
>
>All warnings (new ones prefixed by >>):
>
>   arch/x86/kernel/process_64.c:812:8: warning: 'sprintf' will always overflow; destination buffer has size 2, but format string expands to at least 3 [-Wformat-overflow]
>     812 |         len = sprintf(buf, "%ld\n", lam_available_bits);
>         |               ^
>>> arch/x86/kernel/process_64.c:827:6: warning: unused variable 'ceiling' [-Wunused-variable]
>     827 |         int ceiling;
>         |             ^~~~~~~
>   2 warnings generated.
>
>
>vim +/ceiling +827 arch/x86/kernel/process_64.c
>
>   815
>   816	/*
>   817	 * Writing a number to this file changes the used lam tag width. Valid values
>   818	 * are 4 bit tag width and 6 bit tag width - the second, non-default one is
>   819	 * meant mostly for debug and shall be deprecated in the future.
>   820	 */
>   821	static ssize_t lam_bits_write_file(struct file *file,
>   822					   const char __user *user_buf, size_t count,
>   823					   loff_t *ppos)
>   824	{
>   825		char buf[32];
>   826		ssize_t len;
> > 827		int ceiling;
>   828		u8 bits;
>   829
>   830		len = min(count, sizeof(buf) - 1);
>   831		if (copy_from_user(buf, user_buf, len))
>   832			return -EFAULT;
>   833
>   834		buf[len] = '\0';
>   835		if (kstrtou8(buf, 0, &bits))
>   836			return -EINVAL;
>   837
>   838		switch (bits) {
>   839		case LAM_DEFAULT_BITS:
>   840		case LAM_MAX_BITS:
>   841			lam_available_bits = bits;
>   842			return count;
>   843		default:
>   844			return -EINVAL;
>   845		}
>   846	}
>   847
>
>--
>0-DAY CI Kernel Test Service
>https://github.com/intel/lkp-tests/wiki

-- 
Kind regards
Maciej Wieczór-Retman