linux-kernel - Re: [PATCH 07/25] mm/csky: Use mm_fault

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Message-ID: <20200618222834.GP76766@xz-x1>
Date:   Thu, 18 Jun 2020 18:28:34 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Guo Ren <guoren@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-csky@...r.kernel.org
Subject: Re: [PATCH 07/25] mm/csky: Use mm_fault_accounting()

On Thu, Jun 18, 2020 at 05:24:30PM -0400, Peter Xu wrote:
> >         /* Major fault */
> >         if ((ret & VM_FAULT_MAJOR) || (flags & FAULT_FLAG_TRIED)) {
> >                 flt = &current->maj_flt;
> >                 event_type = PERF_COUNT_SW_PAGE_FAULTS_MAJ;
> >         } else {
> >                 flt = &current->min_flt;
> >                 event_type = PERF_COUNT_SW_PAGE_FAULTS_MIN;
> >         }
> >         *flt++;
> >         if (regs)
> >                 perf_sw_event(event_type, 1, regs, address);

Sadly, this line seems to fail the compilation:

  CC      mm/memory.o
In file included from ././include/linux/compiler_types.h:68,
                 from <command-line>:                      
./arch/x86/include/asm/jump_label.h: In function ‘handle_mm_fault’:
./include/linux/compiler-gcc.h:120:38: warning: ‘asm’ operand 0 probably does not match constraints
  120 | #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
      |                                      ^~~
./arch/x86/include/asm/jump_label.h:25:2: note: in expansion of macro ‘asm_volatile_goto’
   25 |  asm_volatile_goto("1:" 
      |  ^~~~~~~~~~~~~~~~~
./include/linux/compiler-gcc.h:120:38: error: impossible constraint in ‘asm’
  120 | #define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
      |                                      ^~~            
./arch/x86/include/asm/jump_label.h:25:2: note: in expansion of macro ‘asm_volatile_goto’
   25 |  asm_volatile_goto("1:"                                                                                                
      |  ^~~~~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:267: mm/memory.o] Error 1
make: *** [Makefile:1729: mm] Error 2

Frankly speaking I have no solid understanding on what's the error about... But
my gut feeling is that it's about the static keys, where perf_sw_event() may
only support static event types (otherwise we won't be able to know whether to
patch the instruction with no-op or a jump?).

I'll go back to the simple version for now, until I know a solution..

Thanks,

-- 
Peter Xu