[RESEND PATCH v4 05/15] x86,fs/resctrl: Introduce architecture hooks to program kernel-mode

[Babu Moger]

Kernel-mode policies defined by enum resctrl_kernel_mode must be applied to
each affected CPU whenever a policy is selected or its scope changes.
Generic resctrl therefore requires an architecture-specific interface to
program allocation and monitoring associations in hardware across a given
CPU mask.

Introduce a helper, resctrl_arch_configure_kmode(),  to handle kernel-mode
programming. On x86/AMD systems, this helper programs the
MSR_IA32_PQR_PLZA_ASSOC register on all online CPUs in the specified mask
via on_each_cpu_mask(). Also provide a no-op stub for MPAM systems.

Generic resctrl does not invoke this hook yet; it will be used when user
space selects a kernel-mode policy or updates the associated CPU set.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v4: Added assign_mon parameter in resctrl_arch_configure_kmode() to program the RMID
    as discussed in below.
    https://lore.kernel.org/lkml/20260605100642.1103628-1-qinyuntan@xxxxxxxxxxxxxxxxx/
    Changed cpumask type to "const struct cpumask *cpu_mask".
    Added MPAM stub to avoid any linking issues when resctrl_arch_configure_kmode()
    is called from FS layer. Thanks to Qinyun.
    Re-wrote the changelog to be generic.
    Updated code comments.

v3: Removed task based PLZA implementation so related changes are removed.
    Removed handling of rmid_en as it is not required. The group type assigned
    will be different so the monitoring part is already taken care.
    Updated the change log with details.
    Removed resctrl_arch_set_kmode() as arch only provides the modes supported.
    It is FS which decided which mode to apply.

v2: Updated the commit message to include the sequence of steps to enable PLZA.
    Added mode code comments for clarity.
    Added kmode to functin names to be generic.
---
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 36 +++++++++++++++++++++++
 drivers/resctrl/mpam_resctrl.c            |  5 ++++
 include/linux/resctrl.h                   | 15 ++++++++++
 3 files changed, 56 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b20e705606b8..025f139434f2 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -131,3 +131,39 @@ int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)
 
 	return 0;
 }
+
+static void resctrl_kmode_set_one_amd(void *arg)
+{
+	union msr_pqr_plza_assoc *plza = arg;
+
+	wrmsrq(MSR_IA32_PQR_PLZA_ASSOC, plza->full);
+}
+
+/*
+ * Program Privilege Level Zero Association (PLZA) on @cpu_mask.
+ *
+ * When @enable is true, CPL 0 allocation traffic on the targeted CPUs uses
+ * @closid from MSR_IA32_PQR_PLZA_ASSOC instead of the CLOSID from
+ * MSR_IA32_PQR_ASSOC. Monitoring is redirected to @rmid only when
+ * @assign_mon is true; otherwise kernel-mode monitoring continues to use the
+ * RMID associated with the current task.
+ *
+ * @cpu_mask:	CPUs whose PLZA MSR should be updated.
+ * @closid:	CLOSID to use for kernel-mode allocation when PLZA is enabled.
+ * @rmid:	RMID to use for kernel-mode monitoring when @assign_mon is true.
+ * @assign_mon:	Whether PLZA should provide the kernel-mode RMID.
+ * @enable:	Whether PLZA should provide the kernel-mode association.
+ */
+void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid, u32 rmid,
+				  bool assign_mon, bool enable)
+{
+	union msr_pqr_plza_assoc plza = { 0 };
+
+	plza.split.rmid = rmid;
+	plza.split.rmid_en = assign_mon;
+	plza.split.closid = closid;
+	plza.split.closid_en = 1;
+	plza.split.plza_en = enable;
+
+	on_each_cpu_mask(cpu_mask, resctrl_kmode_set_one_amd, &plza, 1);
+}
diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index 226ff6f532fa..630b6cfc0269 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -158,6 +158,11 @@ bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r)
 	return false;
 }
 
+void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid,
+				  u32 rmid, bool assign_mon, bool enable)
+{
+}
+
 void resctrl_arch_pre_mount(void)
 {
 }
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index c7abed51cd5f..47db34dd167e 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -734,6 +734,21 @@ enum resctrl_kernel_mode {
 
 #define RESCTRL_NUM_KERNEL_MODES (RESCTRL_KMODE_LAST + 1)
 
+/**
+ * resctrl_arch_configure_kmode() - Program kernel-mode association on CPUs
+ * @cpu_mask:	CPUs to update; the architecture applies the change on the
+ *		online subset of this mask.
+ * @closid:	Allocation class for kernel-mode traffic. On x86 this is the
+ *		CLOSID programmed when allocation is assigned for kernel work.
+ * @rmid:	Monitoring context for kernel-mode traffic. On x86 this is the
+ *		RMID programmed when monitoring is assigned for kernel work.
+ * @assign_mon:	true to assign @rmid for kernel work; false to inherit
+ *		monitoring from the user task.
+ * @enable:	true to enable kernel-mode association on the targeted CPUs.
+ */
+void resctrl_arch_configure_kmode(const struct cpumask *cpu_mask, u32 closid, u32 rmid,
+				  bool assign_mon, bool enable);
+
 extern unsigned int resctrl_rmid_realloc_threshold;
 extern unsigned int resctrl_rmid_realloc_limit;
 
-- 
2.43.0