powerpc/32e: Ignore ESR in instruction storage interrupt handler

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: [email protected] # v5.12+
Reported-by: Jacques de Laval <[email protected]>
Signed-off-by: Nicholas Piggin <[email protected]>
Tested-by: Jacques de Laval <[email protected]>
Reviewed-by: Christophe Leroy <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index e5503420b6c6da576ec6ce7fa994bb6ffc4c5b87..ef8d1b1c234e7a4099a2c1e8e4802fd5aa3f3d9c 100644 (file)
--- 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