Messages in this thread Patch in this message | | | From | James Morse <> | Subject | [PATCH v5 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted | Date | Fri, 28 Jul 2023 16:42:42 +0000 |
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resctrl_arch_rmid_read() could be called by resctrl in process context, and then called by the PMU driver from irq context on the same CPU. This could cause struct arch_mbm_state's prev_msr value to go backwards, leading to the chunks value being incremented multiple times.
The struct arch_mbm_state holds both the previous msr value, and a count of the number of chunks. These two fields need to be updated atomically. Similarly __rmid_read() must write to one MSR and read from another, this must be proteted from re-entrance.
Read the prev_msr before accessing the hardware, and cmpxchg() the value back. If the value has changed, the whole thing is re-attempted. To protect the MSR, __rmid_read() will retry reads for QM_CTR if QM_EVTSEL has changed from the selected value.
Signed-off-by: James Morse <james.morse@arm.com>
--- Changes since v4: * Added retry loop in __rmid_read() to protect the CPU MSRs. --- arch/x86/kernel/cpu/resctrl/internal.h | 5 +-- arch/x86/kernel/cpu/resctrl/monitor.c | 45 ++++++++++++++++++++------ 2 files changed, 38 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h index a32d307292a1..7012f42a82ee 100644 --- a/arch/x86/kernel/cpu/resctrl/internal.h +++ b/arch/x86/kernel/cpu/resctrl/internal.h @@ -2,6 +2,7 @@ #ifndef _ASM_X86_RESCTRL_INTERNAL_H #define _ASM_X86_RESCTRL_INTERNAL_H +#include <linux/atomic.h> #include <linux/resctrl.h> #include <linux/sched.h> #include <linux/kernfs.h> @@ -338,8 +339,8 @@ struct mbm_state { * find this struct. */ struct arch_mbm_state { - u64 chunks; - u64 prev_msr; + atomic64_t chunks; + atomic64_t prev_msr; }; /** diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c index f0670795b446..62350bbd23e0 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -16,6 +16,7 @@ */ #include <linux/module.h> +#include <linux/percpu.h> #include <linux/sizes.h> #include <linux/slab.h> @@ -24,6 +25,9 @@ #include "internal.h" +/* Sequence number for writes to IA32 QM_EVTSEL */ +static DEFINE_PER_CPU(u64, qm_evtsel_seq); + struct rmid_entry { /* * Some architectures's resctrl_arch_rmid_read() needs the CLOSID value @@ -178,7 +182,7 @@ static inline struct rmid_entry *__rmid_entry(u32 idx) static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val) { - u64 msr_val; + u64 msr_val, seq; /* * As per the SDM, when IA32_QM_EVTSEL.EvtID (bits 7:0) is configured @@ -187,9 +191,16 @@ static int __rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val) * 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. + * A per-cpu sequence counter is incremented each time QM_EVTSEL is + * written. This is used to detect if this function was interrupted by + * another call without re-reading the MSRs. Retry the MSR read when + * this happens as the QM_CTR value may belong to a different event. */ - wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid); - rdmsrl(MSR_IA32_QM_CTR, msr_val); + do { + seq = this_cpu_inc_return(qm_evtsel_seq); + wrmsr(MSR_IA32_QM_EVTSEL, eventid, rmid); + rdmsrl(MSR_IA32_QM_CTR, msr_val); + } while (seq != this_cpu_read(qm_evtsel_seq)); if (msr_val & RMID_VAL_ERROR) return -EIO; @@ -225,13 +236,15 @@ void resctrl_arch_reset_rmid(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; am = get_arch_mbm_state(hw_dom, rmid, eventid); if (am) { memset(am, 0, sizeof(*am)); /* Record any initial, non-zero count value. */ - __rmid_read(rmid, eventid, &am->prev_msr); + __rmid_read(rmid, eventid, &msr_val); + atomic64_set(&am->prev_msr, msr_val); } } @@ -266,23 +279,35 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d, { struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d); + u64 start_msr_val, old_msr_val, msr_val, chunks; struct arch_mbm_state *am; - u64 msr_val, chunks; - int ret; + int ret = 0; if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask)) return -EINVAL; +interrupted: + am = get_arch_mbm_state(hw_dom, rmid, eventid); + if (am) + start_msr_val = atomic64_read(&am->prev_msr); + ret = __rmid_read(rmid, eventid, &msr_val); if (ret) return ret; am = get_arch_mbm_state(hw_dom, rmid, eventid); if (am) { - am->chunks += mbm_overflow_count(am->prev_msr, msr_val, - hw_res->mbm_width); - chunks = get_corrected_mbm_count(rmid, am->chunks); - am->prev_msr = msr_val; + old_msr_val = atomic64_cmpxchg(&am->prev_msr, start_msr_val, + msr_val); + if (old_msr_val != start_msr_val) + goto interrupted; + + chunks = mbm_overflow_count(start_msr_val, msr_val, + hw_res->mbm_width); + atomic64_add(chunks, &am->chunks); + + chunks = get_corrected_mbm_count(rmid, + atomic64_read(&am->chunks)); } else { chunks = msr_val; } -- 2.39.2
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