Commit 3d2ffcdd authored by Ravi Bangoria's avatar Ravi Bangoria Committed by Michael Ellerman
Browse files

powerpc/watchpoint: Workaround P10 DD1 issue with VSX-32 byte instructions 



POWER10 DD1 has an issue where it generates watchpoint exceptions when
it shouldn't. The conditions where this occur are:

 - octword op
 - ending address of DAWR range is less than starting address of op
 - those addresses need to be in the same or in two consecutive 512B
   blocks
 - 'op address + 64B' generates an address that has a carry into bit
   52 (crosses 2K boundary)

Handle such spurious exception by considering them as extraneous and
emulating/single-steeping instruction without generating an event.

[ravi: Fixed build warning reported by lkp@intel.com]
Signed-off-by: default avatarRavi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201106045650.278987-1-ravi.bangoria@linux.ibm.com
parent 35785b29

arch/powerpc/kernel/hw_breakpoint.c

+65 −2
Original line number Diff line number Diff line
@@ -499,6 +499,11 @@ static bool is_larx_stcx_instr(int type) 
	return type == LARX || type == STCX;

}



static bool is_octword_vsx_instr(int type, int size)

{

	return ((type == LOAD_VSX || type == STORE_VSX) && size == 32);

}



/*

 * We've failed in reliably handling the hw-breakpoint. Unregister

 * it and throw a warning message to let the user know about it.
@@ -549,6 +554,58 @@ static bool stepping_handler(struct pt_regs *regs, struct perf_event **bp, 
	return true;

}



static void handle_p10dd1_spurious_exception(struct arch_hw_breakpoint **info,

					     int *hit, unsigned long ea)

{

	int i;

	unsigned long hw_end_addr;



	/*

	 * Handle spurious exception only when any bp_per_reg is set.

	 * Otherwise this might be created by xmon and not actually a

	 * spurious exception.

	 */

	for (i = 0; i < nr_wp_slots(); i++) {

		if (!info[i])

			continue;



		hw_end_addr = ALIGN(info[i]->address + info[i]->len, HW_BREAKPOINT_SIZE);



		/*

		 * Ending address of DAWR range is less than starting

		 * address of op.

		 */

		if ((hw_end_addr - 1) >= ea)

			continue;



		/*

		 * Those addresses need to be in the same or in two

		 * consecutive 512B blocks;

		 */

		if (((hw_end_addr - 1) >> 10) != (ea >> 10))

			continue;



		/*

		 * 'op address + 64B' generates an address that has a

		 * carry into bit 52 (crosses 2K boundary).

		 */

		if ((ea & 0x800) == ((ea + 64) & 0x800))

			continue;



		break;

	}



	if (i == nr_wp_slots())

		return;



	for (i = 0; i < nr_wp_slots(); i++) {

		if (info[i]) {

			hit[i] = 1;

			info[i]->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;

		}

	}

}



int hw_breakpoint_handler(struct die_args *args)

{

	bool err = false;
@@ -607,9 +664,15 @@ int hw_breakpoint_handler(struct die_args *args) 
		goto reset;



	if (!nr_hit) {

		/* Workaround for Power10 DD1 */

		if (!IS_ENABLED(CONFIG_PPC_8xx) && mfspr(SPRN_PVR) == 0x800100 &&

		    is_octword_vsx_instr(type, size)) {

			handle_p10dd1_spurious_exception(info, hit, ea);

		} else {

			rc = NOTIFY_DONE;

			goto out;

		}

	}



	/*

	 * Return early after invoking user-callback function without restoring