Re: [PATCH v11 12/18] x86/fsgsbase/64: move save_fsgs to header file

[kbuild test robot <lkp@intel.com>]

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Hi Sasha,

I love your patch! Yet something to improve:

[auto build test ERROR on tip/x86/asm]
[also build test ERROR on tip/auto-latest linus/master tip/x86/core v5.7-rc4 next-20200508]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Sasha-Levin/Enable-FSGSBASE-instructions/20200510-032805
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 2ce0d7f9766f0e49bb54f149c77bae89464932fb
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@intel.com>

All error/warnings (new ones prefixed by >>):

   In file included from arch/x86/include/uapi/asm/ptrace.h:6:0,
                    from arch/x86/include/asm/ptrace.h:7,
                    from arch/x86/include/asm/math_emu.h:5,
                    from arch/x86/include/asm/processor.h:13,
                    from arch/x86/include/asm/cpufeature.h:5,
                    from arch/x86/include/asm/thread_info.h:53,
                    from include/linux/thread_info.h:38,
                    from arch/x86/include/asm/preempt.h:7,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:51,
                    from include/linux/mmzone.h:8,
                    from include/linux/gfp.h:6,
                    from include/linux/mm.h:10,
                    from arch/x86/kernel/process.c:6:
>> arch/x86/include/uapi/asm/ptrace-abi.h:16:12: error: expected identifier before numeric constant
    #define FS 9
               ^
>> arch/x86/kernel/process.h:42:2: note: in expansion of macro 'FS'
     FS,
     ^~
   In file included from arch/x86/kernel/process.c:46:0:
   arch/x86/kernel/process.h: In function 'save_base_legacy':
>> arch/x86/kernel/process.h:85:18: error: 'struct thread_struct' has no member named 'fsbase'
       prev_p->thread.fsbase = 0;
                     ^
>> arch/x86/kernel/process.h:87:18: error: 'struct thread_struct' has no member named 'gsbase'
       prev_p->thread.gsbase = 0;
                     ^
   In file included from arch/x86/include/asm/ptrace.h:5:0,
                    from arch/x86/include/asm/math_emu.h:5,
                    from arch/x86/include/asm/processor.h:13,
                    from arch/x86/include/asm/cpufeature.h:5,
                    from arch/x86/include/asm/thread_info.h:53,
                    from include/linux/thread_info.h:38,
                    from arch/x86/include/asm/preempt.h:7,
                    from include/linux/preempt.h:78,
                    from include/linux/spinlock.h:51,
                    from include/linux/mmzone.h:8,
                    from include/linux/gfp.h:6,
                    from include/linux/mm.h:10,
                    from arch/x86/kernel/process.c:6:
   arch/x86/kernel/process.h: In function 'save_fsgs':
>> arch/x86/kernel/process.h:93:30: error: 'struct thread_struct' has no member named 'fsindex'
     savesegment(fs, task->thread.fsindex);
                                 ^
   arch/x86/include/asm/segment.h:368:32: note: in definition of macro 'savesegment'
     asm("mov %%" #seg ",%0":"=r" (value) : : "memory")
                                   ^~~~~
>> arch/x86/kernel/process.h:94:30: error: 'struct thread_struct' has no member named 'gsindex'
     savesegment(gs, task->thread.gsindex);
                                 ^
   arch/x86/include/asm/segment.h:368:32: note: in definition of macro 'savesegment'
     asm("mov %%" #seg ",%0":"=r" (value) : : "memory")
                                   ^~~~~
   In file included from arch/x86/kernel/process.c:46:0:
   arch/x86/kernel/process.h:101:15: error: 'struct thread_struct' has no member named 'fsbase'
      task->thread.fsbase = rdfsbase();
                  ^
>> arch/x86/kernel/process.h:101:25: error: implicit declaration of function 'rdfsbase'; did you mean 'rb_erase'? [-Werror=implicit-function-declaration]
      task->thread.fsbase = rdfsbase();
                            ^~~~~~~~
                            rb_erase
   arch/x86/kernel/process.h:102:15: error: 'struct thread_struct' has no member named 'gsbase'
      task->thread.gsbase = x86_gsbase_read_cpu_inactive();
                  ^
>> arch/x86/kernel/process.h:102:25: error: implicit declaration of function 'x86_gsbase_read_cpu_inactive' [-Werror=implicit-function-declaration]
      task->thread.gsbase = x86_gsbase_read_cpu_inactive();
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   arch/x86/kernel/process.h:104:38: error: 'struct thread_struct' has no member named 'fsindex'
      save_base_legacy(task, task->thread.fsindex, FS);
                                         ^
   arch/x86/kernel/process.h:105:38: error: 'struct thread_struct' has no member named 'gsindex'
      save_base_legacy(task, task->thread.gsindex, GS);
                                         ^
   cc1: some warnings being treated as errors

vim +85 arch/x86/kernel/process.h

    40	
    41	enum which_selector {
  > 42		FS,
    43		GS
    44	};
    45	
    46	/*
    47	 * Saves the FS or GS base for an outgoing thread if FSGSBASE extensions are
    48	 * not available.  The goal is to be reasonably fast on non-FSGSBASE systems.
    49	 * It's forcibly inlined because it'll generate better code and this function
    50	 * is hot.
    51	 */
    52	static __always_inline void save_base_legacy(struct task_struct *prev_p,
    53	                                             unsigned short selector,
    54	                                             enum which_selector which)
    55	{
    56		if (likely(selector == 0)) {
    57			/*
    58			 * On Intel (without X86_BUG_NULL_SEG), the segment base could
    59			 * be the pre-existing saved base or it could be zero.  On AMD
    60			 * (with X86_BUG_NULL_SEG), the segment base could be almost
    61			 * anything.
    62			 *
    63			 * This branch is very hot (it's hit twice on almost every
    64			 * context switch between 64-bit programs), and avoiding
    65			 * the RDMSR helps a lot, so we just assume that whatever
    66			 * value is already saved is correct.  This matches historical
    67			 * Linux behavior, so it won't break existing applications.
    68			 *
    69			 * To avoid leaking state, on non-X86_BUG_NULL_SEG CPUs, if we
    70			 * report that the base is zero, it needs to actually be zero:
    71			 * see the corresponding logic in load_seg_legacy.
    72			 */
    73		} else {
    74			/*
    75			 * If the selector is 1, 2, or 3, then the base is zero on
    76			 * !X86_BUG_NULL_SEG CPUs and could be anything on
    77			 * X86_BUG_NULL_SEG CPUs.  In the latter case, Linux
    78			 * has never attempted to preserve the base across context
    79			 * switches.
    80			 *
    81			 * If selector > 3, then it refers to a real segment, and
    82			 * saving the base isn't necessary.
    83			 */
    84			if (which == FS)
  > 85				prev_p->thread.fsbase = 0;
    86			else
  > 87				prev_p->thread.gsbase = 0;
    88		}
    89	}
    90	
    91	static __always_inline void save_fsgs(struct task_struct *task)
    92	{
  > 93		savesegment(fs, task->thread.fsindex);
  > 94		savesegment(gs, task->thread.gsindex);
    95		if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
    96			/*
    97			 * If FSGSBASE is enabled, we can't make any useful guesses
    98			 * about the base, and user code expects us to save the current
    99			 * value.  Fortunately, reading the base directly is efficient.
   100			 */
 > 101			task->thread.fsbase = rdfsbase();
 > 102			task->thread.gsbase = x86_gsbase_read_cpu_inactive();

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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