Messages in this thread Patch in this message | | | From | James Morse <> | Subject | [PATCH v4 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted | Date | Thu, 25 May 2023 18:01:57 +0000 |
| |
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.
Read the prev_msr before accessing the hardware, and cmpxchg() the value back. If the value has changed, the whole thing is re-attempted.
Signed-off-by: James Morse <james.morse@arm.com> --- arch/x86/kernel/cpu/resctrl/internal.h | 5 +++-- arch/x86/kernel/cpu/resctrl/monitor.c | 28 +++++++++++++++++++------- 2 files changed, 24 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h index 6f18cf26988c..7960366b9434 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 e267869d60d5..1f470e55d555 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -225,13 +225,15 @@ 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 +268,35 @@ 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
| |