diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index 19e4744b6eba..6530f1b8874d 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -1377,6 +1377,7 @@ void facility_unavailable_exception(struct pt_regs *regs) }; char *facility = "unknown"; u64 value; + u32 instword, rd; u8 status; bool hv; @@ -1388,12 +1389,46 @@ void facility_unavailable_exception(struct pt_regs *regs) status = value >> 56; if (status == FSCR_DSCR_LG) { - /* User is acessing the DSCR. Set the inherit bit and allow - * the user to set it directly in future by setting via the - * FSCR DSCR bit. We always leave HFSCR DSCR set. + /* + * User is accessing the DSCR register using the problem + * state only SPR number (0x03) either through a mfspr or + * a mtspr instruction. If it is a write attempt through + * a mtspr, then we set the inherit bit. This also allows + * the user to write or read the register directly in the + * future by setting via the FSCR DSCR bit. But in case it + * is a read DSCR attempt through a mfspr instruction, we + * just emulate the instruction instead. This code path will + * always emulate all the mfspr instructions till the user + * has attempted atleast one mtspr instruction. This way it + * preserves the same behaviour when the user is accessing + * the DSCR through privilege level only SPR number (0x11) + * which is emulated through illegal instruction exception. + * We always leave HFSCR DSCR set. */ - current->thread.dscr_inherit = 1; - mtspr(SPRN_FSCR, value | FSCR_DSCR); + if (get_user(instword, (u32 __user *)(regs->nip))) { + pr_err("Failed to fetch the user instruction\n"); + return; + } + + /* Write into DSCR (mtspr 0x03, RS) */ + if ((instword & PPC_INST_MTSPR_DSCR_USER_MASK) + == PPC_INST_MTSPR_DSCR_USER) { + rd = (instword >> 21) & 0x1f; + current->thread.dscr = regs->gpr[rd]; + current->thread.dscr_inherit = 1; + mtspr(SPRN_FSCR, value | FSCR_DSCR); + } + + /* Read from DSCR (mfspr RT, 0x03) */ + if ((instword & PPC_INST_MFSPR_DSCR_USER_MASK) + == PPC_INST_MFSPR_DSCR_USER) { + if (emulate_instruction(regs)) { + pr_err("DSCR based mfspr emulation failed\n"); + return; + } + regs->nip += 4; + emulate_single_step(regs); + } return; }