On Thu, 12 Apr 2018 15:53:52 +1000 Michael Ellerman <m...@ellerman.id.au> wrote:
> 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. > Reviewed-by: Nicholas Piggin <npig...@gmail.com> > Fixes: d4748276ae14 ("powerpc/64s: Improve local TLB flush for boot and MCE > on POWER9") > Cc: sta...@vger.kernel.org # v4.16+ > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > --- > arch/powerpc/mm/tlb-radix.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c > index 2fba6170ab3f..a5d7309c2d05 100644 > --- a/arch/powerpc/mm/tlb-radix.c > +++ b/arch/powerpc/mm/tlb-radix.c > @@ -33,13 +33,12 @@ static inline void tlbiel_radix_set_isa300(unsigned int > set, unsigned int is, > { > unsigned long rb; > unsigned long rs; > - unsigned int r = 1; /* radix format */ > > rb = (set << PPC_BITLSHIFT(51)) | (is << PPC_BITLSHIFT(53)); > rs = ((unsigned long)pid << PPC_BITLSHIFT(31)); > > - asm volatile(PPC_TLBIEL(%0, %1, %2, %3, %4) > - : : "r"(rb), "r"(rs), "i"(ric), "i"(prs), "r"(r) > + asm volatile(PPC_TLBIEL(%0, %1, %2, %3, 1) > + : : "r"(rb), "r"(rs), "i"(ric), "i"(prs) > : "memory"); > } >