Commit 8c63c4af authored by Ravi Bangoria's avatar Ravi Bangoria Committed by Peter Zijlstra
Browse files

perf/amd/ibs: Enable RIP bit63 hardware filtering 



IBS on future hardware adds the ability to filter IBS events by examining
RIP bit 63. Because Linux kernel addresses always have bit 63 set while
user-space addresses never do, this capability can be used as a privilege
filter.

So far, IBS supports privilege filtering in software (swfilt=1), where
samples are dropped in the NMI handler. The RIP bit63 hardware filter
enables IBS to be usable by unprivileged users without passing swfilt
flag. So, swfilt flag will silently be ignored when the hardware
filtering capability is present.

Example (non-root user):
  $ perf record -e ibs_op//u -- <workload>

Signed-off-by: default avatarRavi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260216042530.1546-6-ravi.bangoria@amd.com
parent 35247fa6

arch/x86/events/amd/ibs.c

+38 −8
Original line number Diff line number Diff line
@@ -321,11 +321,6 @@ static int perf_ibs_init(struct perf_event *event) 
	    event->attr.exclude_idle)

		return -EINVAL;



	if (!(event->attr.config2 & IBS_SW_FILTER_MASK) &&

	    (event->attr.exclude_kernel || event->attr.exclude_user ||

	     event->attr.exclude_hv))

		return -EINVAL;



	ret = validate_group(event);

	if (ret)

		return ret;
@@ -338,6 +333,32 @@ static int perf_ibs_init(struct perf_event *event) 
		hwc->extra_reg.reg = perf_ibs->msr2;

	}



	if (ibs_caps & IBS_CAPS_BIT63_FILTER) {

		if (perf_ibs == &perf_ibs_fetch) {

			if (event->attr.exclude_kernel) {

				hwc->extra_reg.config |= IBS_FETCH_2_EXCL_RIP_63_EQ_1;

				hwc->extra_reg.reg = perf_ibs->msr2;

			}

			if (event->attr.exclude_user) {

				hwc->extra_reg.config |= IBS_FETCH_2_EXCL_RIP_63_EQ_0;

				hwc->extra_reg.reg = perf_ibs->msr2;

			}

		} else {

			if (event->attr.exclude_kernel) {

				hwc->extra_reg.config |= IBS_OP_2_EXCL_RIP_63_EQ_1;

				hwc->extra_reg.reg = perf_ibs->msr2;

			}

			if (event->attr.exclude_user) {

				hwc->extra_reg.config |= IBS_OP_2_EXCL_RIP_63_EQ_0;

				hwc->extra_reg.reg = perf_ibs->msr2;

			}

		}

	} else if (!(event->attr.config2 & IBS_SW_FILTER_MASK) &&

		   (event->attr.exclude_kernel || event->attr.exclude_user ||

		    event->attr.exclude_hv)) {

		return -EINVAL;

	}



	if (hwc->sample_period) {

		if (config & perf_ibs->cnt_mask)

			/* raw max_cnt may not be set */
@@ -1280,7 +1301,7 @@ static bool perf_ibs_is_kernel_br_target(struct perf_event *event, 
			op_data.op_brn_ret && kernel_ip(br_target));

}



static bool perf_ibs_swfilt_discard(struct perf_ibs *perf_ibs, struct perf_event *event,

static bool perf_ibs_discard_sample(struct perf_ibs *perf_ibs, struct perf_event *event,

				    struct pt_regs *regs, struct perf_ibs_data *ibs_data,

				    int br_target_idx)

{
@@ -1435,8 +1456,9 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs) 
		regs.flags |= PERF_EFLAGS_EXACT;

	}



	if ((event->attr.config2 & IBS_SW_FILTER_MASK) &&

	    perf_ibs_swfilt_discard(perf_ibs, event, &regs, &ibs_data, br_target_idx)) {

	if (((ibs_caps & IBS_CAPS_BIT63_FILTER) ||

	     (event->attr.config2 & IBS_SW_FILTER_MASK)) &&

	    perf_ibs_discard_sample(perf_ibs, event, &regs, &ibs_data, br_target_idx)) {

		throttle = perf_event_account_interrupt(event);

		goto out;

	}
@@ -1899,6 +1921,14 @@ static __init int amd_ibs_init(void) 


	perf_ibs_pm_init();



#ifdef CONFIG_X86_32

	/*

	 * IBS_CAPS_BIT63_FILTER is used for exclude_kernel/user filtering,

	 * which obviously won't work for 32 bit kernel.

	 */

	caps &= ~IBS_CAPS_BIT63_FILTER;

#endif



	ibs_caps = caps;

	/* make ibs_caps visible to other cpus: */

	smp_mb();