[PATCH] x86/resctrl: Preserve CDP enable over cpuhp

[James Morse <james.morse@arm.com>]

Resctrl assumes that all cpus are online when the filesystem is
mounted, and that cpus remember their CDP-enabled state over cpu
hotplug.

This goes wrong when resctrl's CDP-enabled state changes while all
the cpus in a domain are offline.

When a domain comes online, enable (or disable!) CDP to match resctrl's
current setting.

Fixes: 5ff193fbde20 ("x86/intel_rdt: Add basic resctrl filesystem support")
Signed-off-by: James Morse <james.morse@arm.com>

---

Seen on a 'Intel(R) Xeon(R) Gold 5120T CPU @ 2.20GHz' from lenovo, taking
all the cores in one package offline, umount/mount to toggle CDP then
bringing them back: the first core to come online still has the old
CDP state.

This will get called more often than is desirable (worst:3/domain)
but this is better than on every cpu in the domain. Unless someone
can spot a better place to hook it in?
---
 arch/x86/kernel/cpu/resctrl/core.c     | 21 +++++++++++++++++++++
 arch/x86/kernel/cpu/resctrl/internal.h |  3 +++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  7 +++++--
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 89049b343c7a..1210cb65e6d3 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -541,6 +541,25 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 	return 0;
 }
 
+/* resctrl's use of CDP may have changed while this domain slept */
+static void domain_reconfigure_cdp(void)
+{
+	bool cdp_enable;
+	struct rdt_resource *r;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	r = &rdt_resources_all[RDT_RESOURCE_L2];
+	cdp_enable = !r->alloc_enabled;
+	if (r->alloc_capable)
+		l2_qos_cfg_update(&cdp_enable);
+
+	r = &rdt_resources_all[RDT_RESOURCE_L3];
+	cdp_enable = !r->alloc_enabled;
+	if (r->alloc_capable)
+		l3_qos_cfg_update(&cdp_enable);
+}
+
 /*
  * domain_add_cpu - Add a cpu to a resource's domain list.
  *
@@ -578,6 +597,8 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
 	d->id = id;
 	cpumask_set_cpu(cpu, &d->cpu_mask);
 
+	domain_reconfigure_cdp();
+
 	if (r->alloc_capable && domain_setup_ctrlval(r, d)) {
 		kfree(d);
 		return;
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 181c992f448c..29c92d3e93f5 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -602,4 +602,7 @@ void __check_limbo(struct rdt_domain *d, bool force_free);
 bool cbm_validate_intel(char *buf, u32 *data, struct rdt_resource *r);
 bool cbm_validate_amd(char *buf, u32 *data, struct rdt_resource *r);
 
+void l3_qos_cfg_update(void *arg);
+void l2_qos_cfg_update(void *arg);
+
 #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 064e9ef44cd6..e11356011a4a 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1804,14 +1804,14 @@ mongroup_create_dir(struct kernfs_node *parent_kn, struct rdtgroup *prgrp,
 	return ret;
 }
 
-static void l3_qos_cfg_update(void *arg)
+void l3_qos_cfg_update(void *arg)
 {
 	bool *enable = arg;
 
 	wrmsrl(MSR_IA32_L3_QOS_CFG, *enable ? L3_QOS_CDP_ENABLE : 0ULL);
 }
 
-static void l2_qos_cfg_update(void *arg)
+void l2_qos_cfg_update(void *arg)
 {
 	bool *enable = arg;
 
@@ -1831,6 +1831,9 @@ static int set_cache_qos_cfg(int level, bool enable)
 	struct rdt_domain *d;
 	int cpu;
 
+	/* CDP state is restored during cpuhp, which takes this lock */
+	lockdep_assert_held(&rdtgroup_mutex);
+
 	if (level == RDT_RESOURCE_L3)
 		update = l3_qos_cfg_update;
 	else if (level == RDT_RESOURCE_L2)
-- 
2.24.1