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    Subject[PATCH v9 15/24] x86/resctrl: Allow arch to allocate memory needed in resctrl_arch_rmid_read()
    Date
    Depending on the number of monitors available, Arm's MPAM may need to
    allocate a monitor prior to reading the counter value. Allocating a
    contended resource may involve sleeping.

    __check_limbo() and mon_event_count() each make multiple calls to
    resctrl_arch_rmid_read(), to avoid extra work on contended systems,
    the allocation should be valid for multiple invocations of
    resctrl_arch_rmid_read().

    The memory or hardware allocated is not specific to a domain.

    Add arch hooks for this allocation, which need calling before
    resctrl_arch_rmid_read(). The allocated monitor is passed to
    resctrl_arch_rmid_read(), then freed again afterwards. The helper
    can be called on any CPU, and can sleep.

    Signed-off-by: James Morse <james.morse@arm.com>
    Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
    Tested-by: Peter Newman <peternewman@google.com>
    Tested-by: Babu Moger <babu.moger@amd.com>
    Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
    Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
    Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
    Reviewed-by: Babu Moger <babu.moger@amd.com>
    ---
    Changes since v3:
    * Expanded comment.
    * Removed stray header include.
    * Reworded commit message.
    * Made ctx a void * instead of an int.

    Changes since v4:
    * Used IS_ERR() in more places.

    Changes since v5:
    * Pass the error back from mon_event_read() as -EINVAL/Unavailable.
    * Add some ratelimited warnings when failing to allocate a mon context

    Changes since v6:
    * Added a newline.

    Changes since v7:
    * Replaced explanation of why the memory allocation should be global as
    the old explanation made no sense now that the patches have changed order.
    ---
    arch/x86/include/asm/resctrl.h | 11 +++++++
    arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 7 +++++
    arch/x86/kernel/cpu/resctrl/internal.h | 1 +
    arch/x86/kernel/cpu/resctrl/monitor.c | 35 +++++++++++++++++++++--
    include/linux/resctrl.h | 5 +++-
    5 files changed, 55 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
    index 1d274dbabc44..29c4cc343787 100644
    --- a/arch/x86/include/asm/resctrl.h
    +++ b/arch/x86/include/asm/resctrl.h
    @@ -136,6 +136,17 @@ static inline u32 resctrl_arch_rmid_idx_encode(u32 ignored, u32 rmid)
    return rmid;
    }

    +/* x86 can always read an rmid, nothing needs allocating */
    +struct rdt_resource;
    +static inline void *resctrl_arch_mon_ctx_alloc(struct rdt_resource *r, int evtid)
    +{
    + might_sleep();
    + return NULL;
    +};
    +
    +static inline void resctrl_arch_mon_ctx_free(struct rdt_resource *r, int evtid,
    + void *ctx) { };
    +
    void resctrl_cpu_detect(struct cpuinfo_x86 *c);

    #else
    diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    index d07f99245851..a033e8e32108 100644
    --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
    @@ -546,6 +546,11 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
    rr->d = d;
    rr->val = 0;
    rr->first = first;
    + rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
    + if (IS_ERR(rr->arch_mon_ctx)) {
    + rr->err = -EINVAL;
    + return;
    + }

    cpu = cpumask_any_housekeeping(&d->cpu_mask);

    @@ -559,6 +564,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
    smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1);
    else
    smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
    +
    + resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
    }

    int rdtgroup_mondata_show(struct seq_file *m, void *arg)
    diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
    index 81f5de916db8..e089d1a1a055 100644
    --- a/arch/x86/kernel/cpu/resctrl/internal.h
    +++ b/arch/x86/kernel/cpu/resctrl/internal.h
    @@ -137,6 +137,7 @@ struct rmid_read {
    bool first;
    int err;
    u64 val;
    + void *arch_mon_ctx;
    };

    extern bool rdt_alloc_capable;
    diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
    index e8aeff6673ea..9b503e6ac490 100644
    --- a/arch/x86/kernel/cpu/resctrl/monitor.c
    +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
    @@ -269,7 +269,7 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width)

    int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
    u32 unused, u32 rmid, enum resctrl_event_id eventid,
    - u64 *val)
    + u64 *val, void *ignored)
    {
    struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
    struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
    @@ -324,9 +324,17 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
    u32 idx_limit = resctrl_arch_system_num_rmid_idx();
    struct rmid_entry *entry;
    u32 idx, cur_idx = 1;
    + void *arch_mon_ctx;
    bool rmid_dirty;
    u64 val = 0;

    + arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, QOS_L3_OCCUP_EVENT_ID);
    + if (IS_ERR(arch_mon_ctx)) {
    + pr_warn_ratelimited("Failed to allocate monitor context: %ld",
    + PTR_ERR(arch_mon_ctx));
    + return;
    + }
    +
    /*
    * Skip RMID 0 and start from RMID 1 and check all the RMIDs that
    * are marked as busy for occupancy < threshold. If the occupancy
    @@ -340,7 +348,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)

    entry = __rmid_entry(idx);
    if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
    - QOS_L3_OCCUP_EVENT_ID, &val)) {
    + QOS_L3_OCCUP_EVENT_ID, &val,
    + arch_mon_ctx)) {
    rmid_dirty = true;
    } else {
    rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
    @@ -353,6 +362,8 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
    }
    cur_idx = idx + 1;
    }
    +
    + resctrl_arch_mon_ctx_free(r, QOS_L3_OCCUP_EVENT_ID, arch_mon_ctx);
    }

    bool has_busy_rmid(struct rdt_domain *d)
    @@ -533,7 +544,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
    }

    rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid, rr->evtid,
    - &tval);
    + &tval, rr->arch_mon_ctx);
    if (rr->err)
    return rr->err;

    @@ -722,11 +733,27 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
    if (is_mbm_total_enabled()) {
    rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
    rr.val = 0;
    + rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
    + if (IS_ERR(rr.arch_mon_ctx)) {
    + pr_warn_ratelimited("Failed to allocate monitor context: %ld",
    + PTR_ERR(rr.arch_mon_ctx));
    + return;
    + }
    +
    __mon_event_count(closid, rmid, &rr);
    +
    + resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
    }
    if (is_mbm_local_enabled()) {
    rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
    rr.val = 0;
    + rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
    + if (IS_ERR(rr.arch_mon_ctx)) {
    + pr_warn_ratelimited("Failed to allocate monitor context: %ld",
    + PTR_ERR(rr.arch_mon_ctx));
    + return;
    + }
    +
    __mon_event_count(closid, rmid, &rr);

    /*
    @@ -736,6 +763,8 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d,
    */
    if (is_mba_sc(NULL))
    mbm_bw_count(closid, rmid, &rr);
    +
    + resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
    }
    }

    diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
    index 8649fc84aac2..bf460c912bf5 100644
    --- a/include/linux/resctrl.h
    +++ b/include/linux/resctrl.h
    @@ -235,6 +235,9 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
    * @rmid: rmid of the counter to read.
    * @eventid: eventid to read, e.g. L3 occupancy.
    * @val: result of the counter read in bytes.
    + * @arch_mon_ctx: An architecture specific value from
    + * resctrl_arch_mon_ctx_alloc(), for MPAM this identifies
    + * the hardware monitor allocated for this read request.
    *
    * Some architectures need to sleep when first programming some of the counters.
    * (specifically: arm64's MPAM cache occupancy counters can return 'not ready'
    @@ -248,7 +251,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d);
    */
    int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
    u32 closid, u32 rmid, enum resctrl_event_id eventid,
    - u64 *val);
    + u64 *val, void *arch_mon_ctx);

    /**
    * resctrl_arch_rmid_read_context_check() - warn about invalid contexts
    --
    2.39.2

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