* [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs
@ 2022-12-14 16:08 Peter Newman
2022-12-14 16:08 ` [PATCH v2 2/2] x86/resctrl: Avoid redundant counter read in __mon_event_count() Peter Newman
2022-12-17 0:59 ` [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs Reinette Chatre
0 siblings, 2 replies; 5+ messages in thread
From: Peter Newman @ 2022-12-14 16:08 UTC (permalink / raw)
To: reinette.chatre, fenghua.yu
Cc: Babu.Moger, bp, dave.hansen, eranian, hpa, james.morse,
linux-kernel, mingo, quic_jiles, tan.shaopeng, tglx, x86,
Peter Newman
When creating a new monitoring group, the RMID allocated for it may have
been used by a group which was previously removed. In this case, the
hardware counters will have non-zero values which should be deducted
from what is reported in the new group's counts.
resctrl_arch_reset_rmid() initializes the prev_msr value for counters to
0, causing the initial count to be charged to the new group. Resurrect
__rmid_read() and use it to initialize prev_msr correctly.
Unlike before, __rmid_read() checks for error bits in the MSR read so
that callers don't need to.
Fixes: 1d81d15db39c ("x86/resctrl: Move mbm_overflow_count() into resctrl_arch_rmid_read()")
Signed-off-by: Peter Newman <peternewman@google.com>
---
arch/x86/kernel/cpu/resctrl/monitor.c | 49 ++++++++++++++++++---------
1 file changed, 33 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index efe0c30d3a12..77538abeb72a 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -146,6 +146,30 @@ static inline struct rmid_entry *__rmid_entry(u32 rmid)
return entry;
}
+static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
+{
+ u64 msr_val;
+
+ /*
+ * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
+ * with a valid event code for supported resource type and the bits
+ * IA32_QM_EVTSEL.RMID (bits 41:32) are configured with valid RMID,
+ * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
+ * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
+ * are error bits.
+ */
+ wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
+ rdmsrl(MSR_IA32_QM_CTR, msr_val);
+
+ if (msr_val & RMID_VAL_ERROR)
+ return -EIO;
+ if (msr_val & RMID_VAL_UNAVAIL)
+ return -EINVAL;
+
+ *val = msr_val;
+ return 0;
+}
+
static struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_domain *hw_dom,
u32 rmid,
enum resctrl_event_id eventid)
@@ -172,8 +196,12 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
struct arch_mbm_state *am;
am = get_arch_mbm_state(hw_dom, rmid, eventid);
- if (am)
+ if (am) {
memset(am, 0, sizeof(*am));
+
+ /* Record any initial, non-zero count value. */
+ __rmid_read(rmid, eventid, &am->prev_msr);
+ }
}
static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
@@ -191,25 +219,14 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
struct arch_mbm_state *am;
u64 msr_val, chunks;
+ int ret;
if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
return -EINVAL;
- /*
- * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
- * with a valid event code for supported resource type and the bits
- * IA32_QM_EVTSEL.RMID (bits 41:32) are configured with valid RMID,
- * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
- * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
- * are error bits.
- */
- wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
- rdmsrl(MSR_IA32_QM_CTR, msr_val);
-
- if (msr_val & RMID_VAL_ERROR)
- return -EIO;
- if (msr_val & RMID_VAL_UNAVAIL)
- return -EINVAL;
+ ret = __rmid_read(rmid, eventid, &msr_val);
+ if (ret)
+ return ret;
am = get_arch_mbm_state(hw_dom, rmid, eventid);
if (am) {
base-commit: 830b3c68c1fb1e9176028d02ef86f3cf76aa2476
--
2.39.0.rc1.256.g54fd8350bd-goog
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2 2/2] x86/resctrl: Avoid redundant counter read in __mon_event_count()
2022-12-14 16:08 [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs Peter Newman
@ 2022-12-14 16:08 ` Peter Newman
2022-12-17 1:10 ` Reinette Chatre
2022-12-17 0:59 ` [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs Reinette Chatre
1 sibling, 1 reply; 5+ messages in thread
From: Peter Newman @ 2022-12-14 16:08 UTC (permalink / raw)
To: reinette.chatre, fenghua.yu
Cc: Babu.Moger, bp, dave.hansen, eranian, hpa, james.morse,
linux-kernel, mingo, quic_jiles, tan.shaopeng, tglx, x86,
Peter Newman
__mon_event_count() does the per-RMID, per-domain work for
user-initiated event count reads and the initialization of new monitor
groups.
In the initialization case, after resctrl_arch_reset_rmid() calls
__rmid_read() to record an initial count for a new monitor group, it
immediately calls resctrl_arch_rmid_read(). This re-read of the hardware
counter is unnecessary.
Following return from resctrl_arch_reset_rmid(), just clear the
mbm_state and return.
Also, move the mbm_state lookup into the rr->first case, as it's not
needed for regular event count reads: the QOS_L3_OCCUP_EVENT_ID case was
redundant with the accumulating logic at the end of the function.
Signed-off-by: Peter Newman <peternewman@google.com>
---
arch/x86/kernel/cpu/resctrl/monitor.c | 43 ++++++++++++---------------
1 file changed, 19 insertions(+), 24 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 77538abeb72a..e708df478077 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -366,41 +366,36 @@ void free_rmid(u32 rmid)
list_add_tail(&entry->list, &rmid_free_lru);
}
+static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
+ enum resctrl_event_id evtid)
+{
+ switch (evtid) {
+ case QOS_L3_MBM_TOTAL_EVENT_ID:
+ return &d->mbm_total[rmid];
+ case QOS_L3_MBM_LOCAL_EVENT_ID:
+ return &d->mbm_local[rmid];
+ default:
+ return NULL;
+ }
+}
+
static int __mon_event_count(u32 rmid, struct rmid_read *rr)
{
struct mbm_state *m;
u64 tval = 0;
- if (rr->first)
+ if (rr->first) {
resctrl_arch_reset_rmid(rr->r, rr->d, rmid, rr->evtid);
+ m = get_mbm_state(rr->d, rmid, rr->evtid);
+ if (m)
+ memset(m, 0, sizeof(struct mbm_state));
+ return 0;
+ }
rr->err = resctrl_arch_rmid_read(rr->r, rr->d, rmid, rr->evtid, &tval);
if (rr->err)
return rr->err;
- switch (rr->evtid) {
- case QOS_L3_OCCUP_EVENT_ID:
- rr->val += tval;
- return 0;
- case QOS_L3_MBM_TOTAL_EVENT_ID:
- m = &rr->d->mbm_total[rmid];
- break;
- case QOS_L3_MBM_LOCAL_EVENT_ID:
- m = &rr->d->mbm_local[rmid];
- break;
- default:
- /*
- * Code would never reach here because an invalid
- * event id would fail in resctrl_arch_rmid_read().
- */
- return -EINVAL;
- }
-
- if (rr->first) {
- memset(m, 0, sizeof(struct mbm_state));
- return 0;
- }
-
rr->val += tval;
return 0;
--
2.39.0.rc1.256.g54fd8350bd-goog
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs
2022-12-14 16:08 [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs Peter Newman
2022-12-14 16:08 ` [PATCH v2 2/2] x86/resctrl: Avoid redundant counter read in __mon_event_count() Peter Newman
@ 2022-12-17 0:59 ` Reinette Chatre
2022-12-19 10:31 ` Peter Newman
1 sibling, 1 reply; 5+ messages in thread
From: Reinette Chatre @ 2022-12-17 0:59 UTC (permalink / raw)
To: Peter Newman, fenghua.yu
Cc: Babu.Moger, bp, dave.hansen, eranian, hpa, james.morse,
linux-kernel, mingo, quic_jiles, tan.shaopeng, tglx, x86
Hi Peter,
On 12/14/2022 8:08 AM, Peter Newman wrote:
> When creating a new monitoring group, the RMID allocated for it may have
> been used by a group which was previously removed. In this case, the
> hardware counters will have non-zero values which should be deducted
> from what is reported in the new group's counts.
>
> resctrl_arch_reset_rmid() initializes the prev_msr value for counters to
> 0, causing the initial count to be charged to the new group. Resurrect
> __rmid_read() and use it to initialize prev_msr correctly.
>
> Unlike before, __rmid_read() checks for error bits in the MSR read so
> that callers don't need to.
>
> Fixes: 1d81d15db39c ("x86/resctrl: Move mbm_overflow_count() into resctrl_arch_rmid_read()")
> Signed-off-by: Peter Newman <peternewman@google.com>
This does look like a candidate for stable?
> ---
It is helpful to have a summary here of what changed since previous version.
> arch/x86/kernel/cpu/resctrl/monitor.c | 49 ++++++++++++++++++---------
> 1 file changed, 33 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index efe0c30d3a12..77538abeb72a 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -146,6 +146,30 @@ static inline struct rmid_entry *__rmid_entry(u32 rmid)
> return entry;
> }
>
> +static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val)
> +{
> + u64 msr_val;
> +
> + /*
> + * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
> + * with a valid event code for supported resource type and the bits
> + * IA32_QM_EVTSEL.RMID (bits 41:32) are configured with valid RMID,
> + * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
> + * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
> + * are error bits.
> + */
> + wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
> + rdmsrl(MSR_IA32_QM_CTR, msr_val);
> +
> + if (msr_val & RMID_VAL_ERROR)
> + return -EIO;
> + if (msr_val & RMID_VAL_UNAVAIL)
> + return -EINVAL;
> +
> + *val = msr_val;
> + return 0;
> +}
> +
> static struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_domain *hw_dom,
> u32 rmid,
> enum resctrl_event_id eventid)
> @@ -172,8 +196,12 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
> struct arch_mbm_state *am;
>
> am = get_arch_mbm_state(hw_dom, rmid, eventid);
> - if (am)
> + if (am) {
> memset(am, 0, sizeof(*am));
> +
> + /* Record any initial, non-zero count value. */
> + __rmid_read(rmid, eventid, &am->prev_msr);
> + }
> }
>
> static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)
> @@ -191,25 +219,14 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
> struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
> struct arch_mbm_state *am;
> u64 msr_val, chunks;
> + int ret;
>
> if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask))
> return -EINVAL;
>
> - /*
> - * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured
> - * with a valid event code for supported resource type and the bits
> - * IA32_QM_EVTSEL.RMID (bits 41:32) are configured with valid RMID,
> - * IA32_QM_CTR.data (bits 61:0) reports the monitored data.
> - * IA32_QM_CTR.Error (bit 63) and IA32_QM_CTR.Unavailable (bit 62)
> - * are error bits.
> - */
> - wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid);
> - rdmsrl(MSR_IA32_QM_CTR, msr_val);
> -
> - if (msr_val & RMID_VAL_ERROR)
> - return -EIO;
> - if (msr_val & RMID_VAL_UNAVAIL)
> - return -EINVAL;
> + ret = __rmid_read(rmid, eventid, &msr_val);
> + if (ret)
> + return ret;
>
> am = get_arch_mbm_state(hw_dom, rmid, eventid);
> if (am) {
>
> base-commit: 830b3c68c1fb1e9176028d02ef86f3cf76aa2476
Thank you very much for catching and fixing this.
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reinette
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 2/2] x86/resctrl: Avoid redundant counter read in __mon_event_count()
2022-12-14 16:08 ` [PATCH v2 2/2] x86/resctrl: Avoid redundant counter read in __mon_event_count() Peter Newman
@ 2022-12-17 1:10 ` Reinette Chatre
0 siblings, 0 replies; 5+ messages in thread
From: Reinette Chatre @ 2022-12-17 1:10 UTC (permalink / raw)
To: Peter Newman, fenghua.yu
Cc: Babu.Moger, bp, dave.hansen, eranian, hpa, james.morse,
linux-kernel, mingo, quic_jiles, tan.shaopeng, tglx, x86
Hi Peter,
On 12/14/2022 8:08 AM, Peter Newman wrote:
> __mon_event_count() does the per-RMID, per-domain work for
> user-initiated event count reads and the initialization of new monitor
> groups.
>
> In the initialization case, after resctrl_arch_reset_rmid() calls
> __rmid_read() to record an initial count for a new monitor group, it
> immediately calls resctrl_arch_rmid_read(). This re-read of the hardware
> counter is unnecessary.
"... and the following computations are ignored by the caller during
initialization."
>
> Following return from resctrl_arch_reset_rmid(), just clear the
> mbm_state and return.
>
> Also, move the mbm_state lookup into the rr->first case, as it's not
> needed for regular event count reads: the QOS_L3_OCCUP_EVENT_ID case was
> redundant with the accumulating logic at the end of the function.
Starting the above with "Also" creates impression that two logical
changes are merged into a single patch. Since this is not the case you
can avoid the impression with something like:
Following return from resctrl_arch_reset_rmid(), just clear the
mbm_state and return. This involves moving the mbm_state lookup into
the rr->first case, as it's not needed for regular event count reads:
the QOS_L3_OCCUP_EVENT_ID case was redundant with the accumulating logic
at the end of the function.
>
> Signed-off-by: Peter Newman <peternewman@google.com>
> ---
> arch/x86/kernel/cpu/resctrl/monitor.c | 43 ++++++++++++---------------
> 1 file changed, 19 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 77538abeb72a..e708df478077 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -366,41 +366,36 @@ void free_rmid(u32 rmid)
> list_add_tail(&entry->list, &rmid_free_lru);
> }
>
> +static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
> + enum resctrl_event_id evtid)
> +{
> + switch (evtid) {
> + case QOS_L3_MBM_TOTAL_EVENT_ID:
> + return &d->mbm_total[rmid];
> + case QOS_L3_MBM_LOCAL_EVENT_ID:
> + return &d->mbm_local[rmid];
> + default:
> + return NULL;
> + }
> +}
> +
> static int __mon_event_count(u32 rmid, struct rmid_read *rr)
> {
> struct mbm_state *m;
> u64 tval = 0;
>
> - if (rr->first)
> + if (rr->first) {
> resctrl_arch_reset_rmid(rr->r, rr->d, rmid, rr->evtid);
> + m = get_mbm_state(rr->d, rmid, rr->evtid);
> + if (m)
> + memset(m, 0, sizeof(struct mbm_state));
> + return 0;
> + }
>
> rr->err = resctrl_arch_rmid_read(rr->r, rr->d, rmid, rr->evtid, &tval);
> if (rr->err)
> return rr->err;
>
> - switch (rr->evtid) {
> - case QOS_L3_OCCUP_EVENT_ID:
> - rr->val += tval;
> - return 0;
> - case QOS_L3_MBM_TOTAL_EVENT_ID:
> - m = &rr->d->mbm_total[rmid];
> - break;
> - case QOS_L3_MBM_LOCAL_EVENT_ID:
> - m = &rr->d->mbm_local[rmid];
> - break;
> - default:
> - /*
> - * Code would never reach here because an invalid
> - * event id would fail in resctrl_arch_rmid_read().
> - */
> - return -EINVAL;
> - }
> -
> - if (rr->first) {
> - memset(m, 0, sizeof(struct mbm_state));
> - return 0;
> - }
> -
> rr->val += tval;
>
> return 0;
Thank you very much.
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reinette
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs
2022-12-17 0:59 ` [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs Reinette Chatre
@ 2022-12-19 10:31 ` Peter Newman
0 siblings, 0 replies; 5+ messages in thread
From: Peter Newman @ 2022-12-19 10:31 UTC (permalink / raw)
To: Reinette Chatre
Cc: fenghua.yu, Babu.Moger, bp, dave.hansen, eranian, hpa,
james.morse, linux-kernel, mingo, quic_jiles, tan.shaopeng, tglx,
x86
Hi Reinette,
On Sat, Dec 17, 2022 at 1:59 AM Reinette Chatre
<reinette.chatre@intel.com> wrote:
> On 12/14/2022 8:08 AM, Peter Newman wrote:
> > When creating a new monitoring group, the RMID allocated for it may have
> > been used by a group which was previously removed. In this case, the
> > hardware counters will have non-zero values which should be deducted
> > from what is reported in the new group's counts.
> >
> > resctrl_arch_reset_rmid() initializes the prev_msr value for counters to
> > 0, causing the initial count to be charged to the new group. Resurrect
> > __rmid_read() and use it to initialize prev_msr correctly.
> >
> > Unlike before, __rmid_read() checks for error bits in the MSR read so
> > that callers don't need to.
> >
> > Fixes: 1d81d15db39c ("x86/resctrl: Move mbm_overflow_count() into resctrl_arch_rmid_read()")
> > Signed-off-by: Peter Newman <peternewman@google.com>
>
> This does look like a candidate for stable?
Yes, this bug is serious and reproducible. Every RMID reuse would
have up to one overflow's-worth of measurement error.
Should I elaborate on the impact more in the changelog?
>
> > ---
>
> It is helpful to have a summary here of what changed since previous version.
ok, I'll add this
> Thank you very much for catching and fixing this.
>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Thanks, Reinette!
-Peter
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-12-19 10:32 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2022-12-17 1:10 ` Reinette Chatre
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