From: Reinette Chatre <reinette.chatre@intel.com>
To: James Morse <james.morse@arm.com>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.com>,
<shameerali.kolothum.thodi@huawei.com>,
D Scott Phillips OS <scott@os.amperecomputing.com>,
<carl@os.amperecomputing.com>, <lcherian@marvell.com>,
<bobo.shaobowang@huawei.com>, <tan.shaopeng@fujitsu.com>,
<xingxin.hx@openanolis.org>, <baolin.wang@linux.alibaba.com>,
Jamie Iles <quic_jiles@quicinc.com>,
Xin Hao <xhao@linux.alibaba.com>, <peternewman@google.com>,
<dfustini@baylibre.com>
Subject: Re: [PATCH v5 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted
Date: Wed, 9 Aug 2023 15:35:25 -0700 [thread overview]
Message-ID: <192aa189-8b08-c8c1-15dc-722e196493f4@intel.com> (raw)
In-Reply-To: <20230728164254.27562-13-james.morse@arm.com>
Hi James,
On 7/28/2023 9:42 AM, James Morse wrote:
> 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.
The changelog is written as a bug report of current behavior.
This does not seem to describe current but instead planned future behavior.
> 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.
proteted -> protected
>
> 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.
The latter part of the sentence does not seem to match with what the
patch does.
>
> 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;
> +
hmmm ... what if interruption occurs here?
> + 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;
> }
Reinette
next prev parent reply other threads:[~2023-08-09 22:35 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-28 16:42 [PATCH v5 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking James Morse
2023-07-28 16:42 ` [PATCH v5 01/24] x86/resctrl: Track the closid with the rmid James Morse
2023-08-09 22:32 ` Reinette Chatre
2023-08-24 16:50 ` James Morse
2023-08-15 0:09 ` Fenghua Yu
2023-07-28 16:42 ` [PATCH v5 02/24] x86/resctrl: Access per-rmid structures by index James Morse
2023-08-09 22:32 ` Reinette Chatre
2023-08-24 16:51 ` James Morse
2023-08-25 0:29 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 03/24] x86/resctrl: Create helper for RMID allocation and mondata dir creation James Morse
2023-08-09 22:32 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare() James Morse
2023-08-15 0:50 ` Fenghua Yu
2023-08-24 16:52 ` James Morse
2023-07-28 16:42 ` [PATCH v5 05/24] x86/resctrl: Allow RMID allocation to be scoped by CLOSID James Morse
2023-08-09 22:33 ` Reinette Chatre
2023-08-15 1:22 ` Fenghua Yu
2023-07-28 16:42 ` [PATCH v5 06/24] x86/resctrl: Track the number of dirty RMID a CLOSID has James Morse
2023-08-09 22:33 ` Reinette Chatre
2023-08-24 16:53 ` James Morse
2023-08-24 22:58 ` Reinette Chatre
2023-08-30 22:32 ` Tony Luck
2023-08-14 23:58 ` Fenghua Yu
2023-08-15 2:37 ` Fenghua Yu
2023-08-24 16:53 ` James Morse
2023-07-28 16:42 ` [PATCH v5 07/24] x86/resctrl: Use set_bit()/clear_bit() instead of open coding James Morse
2023-07-28 16:42 ` [PATCH v5 08/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid James Morse
2023-08-15 2:59 ` Fenghua Yu
2023-08-24 16:54 ` James Morse
2023-07-28 16:42 ` [PATCH v5 09/24] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers James Morse
2023-07-28 16:42 ` [PATCH v5 10/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef James Morse
2023-08-09 22:34 ` Reinette Chatre
2023-08-24 16:55 ` James Morse
2023-08-25 0:43 ` Reinette Chatre
2023-09-08 15:58 ` James Morse
2023-07-28 16:42 ` [PATCH v5 11/24] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow James Morse
2023-07-28 16:42 ` [PATCH v5 12/24] x86/resctrl: Make resctrl_arch_rmid_read() retry when it is interrupted James Morse
2023-08-09 22:35 ` Reinette Chatre [this message]
2023-08-24 16:55 ` James Morse
2023-08-24 23:01 ` Reinette Chatre
2023-09-08 15:58 ` James Morse
2023-09-08 20:15 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 13/24] x86/resctrl: Queue mon_event_read() instead of sending an IPI James Morse
2023-07-28 16:42 ` [PATCH v5 14/24] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep James Morse
2023-08-09 22:36 ` Reinette Chatre
2023-08-24 16:56 ` James Morse
2023-08-24 23:02 ` Reinette Chatre
2023-09-08 15:58 ` James Morse
2023-09-08 20:15 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read() James Morse
2023-08-09 22:37 ` Reinette Chatre
2023-08-24 16:56 ` James Morse
2023-08-24 23:04 ` Reinette Chatre
2023-09-15 17:37 ` James Morse
2023-07-28 16:42 ` [PATCH v5 16/24] x86/resctrl: Make resctrl_mounted checks explicit James Morse
2023-07-28 16:42 ` [PATCH v5 17/24] x86/resctrl: Move alloc/mon static keys into helpers James Morse
2023-07-28 16:42 ` [PATCH v5 18/24] x86/resctrl: Make rdt_enable_key the arch's decision to switch James Morse
2023-07-28 16:42 ` [PATCH v5 19/24] x86/resctrl: Add helpers for system wide mon/alloc capable James Morse
2023-08-17 18:34 ` Fenghua Yu
2023-08-24 16:57 ` James Morse
2023-07-28 16:42 ` [PATCH v5 20/24] x86/resctrl: Add cpu online callback for resctrl work James Morse
2023-08-09 22:38 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 21/24] x86/resctrl: Allow overflow/limbo handlers to be scheduled on any-but cpu James Morse
2023-08-09 22:38 ` Reinette Chatre
2023-08-24 16:57 ` James Morse
2023-07-28 16:42 ` [PATCH v5 22/24] x86/resctrl: Add cpu offline callback for resctrl work James Morse
2023-07-28 16:42 ` [PATCH v5 23/24] x86/resctrl: Move domain helper migration into resctrl_offline_cpu() James Morse
2023-08-09 22:39 ` Reinette Chatre
2023-07-28 16:42 ` [PATCH v5 24/24] x86/resctrl: Separate arch and fs resctrl locks James Morse
2023-08-09 22:41 ` Reinette Chatre
2023-08-24 16:57 ` James Morse
2023-08-18 22:05 ` Fenghua Yu
2023-08-24 16:58 ` James Morse
2023-08-03 7:34 ` [PATCH v5 00/24] x86/resctrl: monitored closid+rmid together, separate arch/fs locking Shaopeng Tan (Fujitsu)
2023-08-24 16:58 ` James Morse
2023-08-22 8:42 ` Peter Newman
2023-08-24 16:58 ` James Morse
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