• Michael Ellerman's avatar
    powerpc/mm/radix: Fix checkstops caused by invalid tlbiel · 2675c13b
    Michael Ellerman authored
    In tlbiel_radix_set_isa300() we use the PPC_TLBIEL() macro to
    construct tlbiel instructions. The instruction takes 5 fields, two of
    which are registers, and the others are constants. But because it's
    constructed with inline asm the compiler doesn't know that.
    
    We got the constraint wrong on the 'r' field, using "r" tells the
    compiler to put the value in a register. The value we then get in the
    macro is the *register number*, not the value of the field.
    
    That means when we mask the register number with 0x1 we get 0 or 1
    depending on which register the compiler happens to put the constant
    in, eg:
    
      li      r10,1
      tlbiel  r8,r9,2,0,0
    
      li      r7,1
      tlbiel  r10,r6,0,0,1
    
    If we're unlucky we might generate an invalid instruction form, for
    example RIC=0, PRS=1 and R=0, tlbiel r8,r7,0,1,0, this has been
    observed to cause machine checks:
    
      Oops: Machine check, sig: 7 [#1]
      CPU: 24 PID: 0 Comm: swapper
      NIP:  00000000000385f4 LR: 000000000100ed00 CTR: 000000000000007f
      REGS: c00000000110bb40 TRAP: 0200
      MSR:  9000000000201003 <SF,HV,ME,RI,LE>  CR: 48002222  XER: 20040000
      CFAR: 00000000000385d0 DAR: 0000000000001c00 DSISR: 00000200 SOFTE: 1
    
    If the machine check happens early in boot while we have MSR_ME=0 it
    will escalate into a checkstop and kill the box entirely.
    
    To fix it we could change the inline asm constraint to "i" which
    tells the compiler the value is a constant. But a better fix is to just
    pass a literal 1 into the macro, which bypasses any problems with inline
    asm constraints.
    
    Fixes: d4748276 ("powerpc/64s: Improve local TLB flush for boot and MCE on POWER9")
    Cc: stable@vger.kernel.org # v4.16+
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
    2675c13b
tlb-radix.c 19.4 KB