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SubjectRe: [PATCH v2 1/2] x86/resctrl: Fix event counts regression in reused RMIDs
From
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

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