From: Nicholas Piggin npiggin@gmail.com
commit 81291383ffde08b23bce75e7d6b2575ce9d3475c upstream.
A e5500 machine running a 32-bit kernel sometimes hangs at boot, seemingly going into an infinite loop of instruction storage interrupts.
The ESR (Exception Syndrome Register) has a value of 0x800000 (store) when this happens, which is likely set by a previous store. An instruction TLB miss interrupt would then leave ESR unchanged, and if no PTE exists it calls directly to the instruction storage interrupt handler without changing ESR.
access_error() does not cause a segfault due to a store to a read-only vma because is_exec is true. Most subsequent fault handling does not check for a write fault on a read-only vma, and might do strange things like create a writeable PTE or call page_mkwrite on a read only vma or file. It's not clear what happens here to cause the infinite faulting in this case, a fault handler failure or low level PTE or TLB handling.
In any case this can be fixed by having the instruction storage interrupt zero regs->dsisr rather than storing the ESR value to it.
Fixes: a01a3f2ddbcd ("powerpc: remove arguments from fault handler functions") Cc: stable@vger.kernel.org # v5.12+ Reported-by: Jacques de Laval jacques.delaval@protonmail.com Signed-off-by: Nicholas Piggin npiggin@gmail.com Tested-by: Jacques de Laval jacques.delaval@protonmail.com Reviewed-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20211028133043.4159501-1-npiggin@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/head_booke.h | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/head_booke.h +++ b/arch/powerpc/kernel/head_booke.h @@ -465,12 +465,21 @@ label: bl do_page_fault; \ b interrupt_return
+/* + * Instruction TLB Error interrupt handlers may call InstructionStorage + * directly without clearing ESR, so the ESR at this point may be left over + * from a prior interrupt. + * + * In any case, do_page_fault for BOOK3E does not use ESR and always expects + * dsisr to be 0. ESR_DST from a prior store in particular would confuse fault + * handling. + */ #define INSTRUCTION_STORAGE_EXCEPTION \ START_EXCEPTION(InstructionStorage) \ - NORMAL_EXCEPTION_PROLOG(0x400, INST_STORAGE); \ - mfspr r5,SPRN_ESR; /* Grab the ESR and save it */ \ + NORMAL_EXCEPTION_PROLOG(0x400, INST_STORAGE); \ + li r5,0; /* Store 0 in regs->esr (dsisr) */ \ stw r5,_ESR(r11); \ - stw r12, _DEAR(r11); /* Pass SRR0 as arg2 */ \ + stw r12, _DEAR(r11); /* Set regs->dear (dar) to SRR0 */ \ prepare_transfer_to_handler; \ bl do_page_fault; \ b interrupt_return