[PATCH v1 20/31] x86/resctrl: Allow an architecture to disable pseudo lock

James Morse
2024-03-21T16:52:34Z

Pseudo-lock relies on knowledge of the micro-architecture to disable
prefetchers etc.

On arm64 these controls are typically secure only, meaning linux can't
access them. Arm's cache-lockdown feature works in a very different
way. Resctrl's pseudo-lock isn't going to be used on arm64 platforms.

Add a Kconfig symbol that can be selected by the architecture. This
enables or disables building of the psuedo_lock.c file, and replaces
the functions with stubs. An additional IS_ENABLED() check is needed
in rdtgroup_mode_write() so that attempting to enable pseudo-lock
reports an "Unknown or unsupported mode" to user-space.

Signed-off-by: James Morse <james.morse@arm.com>
---
arch/x86/Kconfig | 7 ++++
arch/x86/kernel/cpu/resctrl/Makefile | 5 +--
arch/x86/kernel/cpu/resctrl/internal.h | 48 +++++++++++++++++++++-----
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 3 +-
4 files changed, 52 insertions(+), 11 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7aed87cbf386..e071e564452e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -481,6 +481,7 @@ config X86_CPU_RESCTRL
depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)
select KERNFS
select PROC_CPU_RESCTRL if PROC_FS
+ select RESCTRL_FS_PSEUDO_LOCK
help
Enable x86 CPU resource control support.

@@ -506,6 +507,12 @@ config X86_FRED
ring transitions and exception/interrupt handling if the
system supports.

+config RESCTRL_FS_PSEUDO_LOCK
+ bool
+ help
+ Software mechanism to pin data in a cache portion using
+ micro-architecture specific knowledge.
+
if X86_32
config X86_BIGSMP
bool "Support for big SMP systems with more than 8 CPUs"
diff --git a/arch/x86/kernel/cpu/resctrl/Makefile b/arch/x86/kernel/cpu/resctrl/Makefile
index 4a06c37b9cf1..0c13b0befd8a 100644
--- a/arch/x86/kernel/cpu/resctrl/Makefile
+++ b/arch/x86/kernel/cpu/resctrl/Makefile
@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_X86_CPU_RESCTRL) += core.o rdtgroup.o monitor.o
-obj-$(CONFIG_X86_CPU_RESCTRL) += ctrlmondata.o pseudo_lock.o
+obj-$(CONFIG_X86_CPU_RESCTRL) += core.o rdtgroup.o monitor.o
+obj-$(CONFIG_X86_CPU_RESCTRL) += ctrlmondata.o
+obj-$(CONFIG_RESCTRL_FS_PSEUDO_LOCK) += pseudo_lock.o
CFLAGS_pseudo_lock.o = -I$(src)
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 238b81d3f64a..d6db15839dc4 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -489,14 +489,6 @@ unsigned int rdtgroup_cbm_to_size(struct rdt_resource *r, struct rdt_domain *d,
unsigned long cbm);
enum rdtgrp_mode rdtgroup_mode_by_closid(int closid);
int rdtgroup_tasks_assigned(struct rdtgroup *r);
-int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
-int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp);
-bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, unsigned long cbm);
-bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d);
-int rdt_pseudo_lock_init(void);
-void rdt_pseudo_lock_release(void);
-int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp);
-void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);
struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
int closids_supported(void);
void closid_free(int closid);
@@ -529,4 +521,44 @@ void rdt_staged_configs_clear(void);
bool closid_allocated(unsigned int closid);
int resctrl_find_cleanest_closid(void);

+#ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
+int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
+int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp);
+bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, unsigned long cbm);
+bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d);
+int rdt_pseudo_lock_init(void);
+void rdt_pseudo_lock_release(void);
+int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp);
+void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);
+#else
+static inline int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, unsigned long cbm)
+{
+ return false;
+}
+
+static inline bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_domain *d)
+{
+ return false;
+}
+
+static inline int rdt_pseudo_lock_init(void) { return 0; }
+static inline void rdt_pseudo_lock_release(void) { }
+static inline int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp) { }
+#endif /* CONFIG_RESCTRL_FS_PSEUDO_LOCK */
+
#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 56a0bfdc11f7..9275d6f8a74e 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1452,7 +1452,8 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
goto out;
}
rdtgrp->mode = RDT_MODE_EXCLUSIVE;
- } else if (!strcmp(buf, "pseudo-locksetup")) {
+ } else if (IS_ENABLED(CONFIG_RESCTRL_FS_PSEUDO_LOCK) &&
+ !strcmp(buf, "pseudo-locksetup")) {
ret = rdtgroup_locksetup_enter(rdtgrp);
if (ret)
goto out;
--
2.39.2