[PATCH v7 04/15] x86/sgx: Implement basic EPC misc cgroup functionality

From: Haitao Huang
Date: Mon Jan 22 2024 - 12:53:42 EST

From: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>

SGX Enclave Page Cache (EPC) memory allocations are separate from normal
RAM allocations, and are managed solely by the SGX subsystem. The
existing cgroup memory controller cannot be used to limit or account for
SGX EPC memory, which is a desirable feature in some environments. For
example, in a Kubernates environment, a user can request certain EPC
quota for a pod but the orchestrator can not enforce the quota to limit
runtime EPC usage of the pod without an EPC cgroup controller.

Utilize the misc controller [admin-guide/cgroup-v2.rst, 5-9. Misc] to
limit and track EPC allocations per cgroup. Earlier patches have added
the "sgx_epc" resource type in the misc cgroup subsystem. Add basic
support in SGX driver as the "sgx_epc" resource provider:

- Set "capacity" of EPC by calling misc_cg_set_capacity()
- Update EPC usage counter, "current", by calling charge and uncharge
APIs for EPC allocation and deallocation, respectively.
- Setup sgx_epc resource type specific callbacks, which perform
initialization and cleanup during cgroup allocation and deallocation,
respectively.

With these changes, the misc cgroup controller enables user to set a hard
limit for EPC usage in the "misc.max" interface file. It reports current
usage in "misc.current", the total EPC memory available in
"misc.capacity", and the number of times EPC usage reached the max limit
in "misc.events".

For now, the EPC cgroup simply blocks additional EPC allocation in
sgx_alloc_epc_page() when the limit is reached. Reclaimable pages are
still tracked in the global active list, only reclaimed by the global
reclaimer when the total free page count is lower than a threshold.

Later patches will reorganize the tracking and reclamation code in the
global reclaimer and implement per-cgroup tracking and reclaiming.

Co-developed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Co-developed-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
---
V7:
- Use a static for root cgroup (Kai)
- Wrap epc_cg field in sgx_epc_page struct with #ifdef (Kai)
- Correct check for charge API return (Kai)
- Start initialization in SGX device driver init (Kai)
- Remove unneeded BUG_ON (Kai)
- Split sgx_get_current_epc_cg() out of sgx_epc_cg_try_charge() (Kai)

V6:
- Split the original large patch"Limit process EPC usage with misc
cgroup controller" and restructure it (Kai)
---
arch/x86/Kconfig | 13 +++++
arch/x86/kernel/cpu/sgx/Makefile | 1 +
arch/x86/kernel/cpu/sgx/epc_cgroup.c | 79 ++++++++++++++++++++++++++++
arch/x86/kernel/cpu/sgx/epc_cgroup.h | 73 +++++++++++++++++++++++++
arch/x86/kernel/cpu/sgx/main.c | 52 +++++++++++++++++-
arch/x86/kernel/cpu/sgx/sgx.h | 5 ++
include/linux/misc_cgroup.h | 2 +
7 files changed, 223 insertions(+), 2 deletions(-)
create mode 100644 arch/x86/kernel/cpu/sgx/epc_cgroup.c
create mode 100644 arch/x86/kernel/cpu/sgx/epc_cgroup.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5edec175b9bf..10c3d1d099b2 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1947,6 +1947,19 @@ config X86_SGX

If unsure, say N.

+config CGROUP_SGX_EPC
+ bool "Miscellaneous Cgroup Controller for Enclave Page Cache (EPC) for Intel SGX"
+ depends on X86_SGX && CGROUP_MISC
+ help
+ Provides control over the EPC footprint of tasks in a cgroup via
+ the Miscellaneous cgroup controller.
+
+ EPC is a subset of regular memory that is usable only by SGX
+ enclaves and is very limited in quantity, e.g. less than 1%
+ of total DRAM.
+
+ Say N if unsure.
+
config X86_USER_SHADOW_STACK
bool "X86 userspace shadow stack"
depends on AS_WRUSS
diff --git a/arch/x86/kernel/cpu/sgx/Makefile b/arch/x86/kernel/cpu/sgx/Makefile
index 9c1656779b2a..12901a488da7 100644
--- a/arch/x86/kernel/cpu/sgx/Makefile
+++ b/arch/x86/kernel/cpu/sgx/Makefile
@@ -4,3 +4,4 @@ obj-y += \
ioctl.o \
main.o
obj-$(CONFIG_X86_SGX_KVM) += virt.o
+obj-$(CONFIG_CGROUP_SGX_EPC) += epc_cgroup.o
diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
new file mode 100644
index 000000000000..938695816a9e
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright(c) 2022 Intel Corporation.
+
+#include <linux/atomic.h>
+#include <linux/kernel.h>
+#include "epc_cgroup.h"
+
+static struct sgx_epc_cgroup epc_cg_root;
+
+/**
+ * sgx_epc_cgroup_try_charge() - try to charge cgroup for a single EPC page
+ *
+ * @epc_cg: The EPC cgroup to be charged for the page.
+ * Return:
+ * * %0 - If successfully charged.
+ * * -errno - for failures.
+ */
+int sgx_epc_cgroup_try_charge(struct sgx_epc_cgroup *epc_cg)
+{
+ if (!epc_cg)
+ return -EINVAL;
+
+ return misc_cg_try_charge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE);
+}
+
+/**
+ * sgx_epc_cgroup_uncharge() - uncharge a cgroup for an EPC page
+ * @epc_cg: The charged epc cgroup
+ */
+void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg)
+{
+ if (!epc_cg)
+ return;
+
+ misc_cg_uncharge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE);
+}
+
+static void sgx_epc_cgroup_free(struct misc_cg *cg)
+{
+ struct sgx_epc_cgroup *epc_cg;
+
+ epc_cg = sgx_epc_cgroup_from_misc_cg(cg);
+ if (!epc_cg)
+ return;
+
+ kfree(epc_cg);
+}
+
+static int sgx_epc_cgroup_alloc(struct misc_cg *cg);
+
+const struct misc_res_ops sgx_epc_cgroup_ops = {
+ .alloc = sgx_epc_cgroup_alloc,
+ .free = sgx_epc_cgroup_free,
+};
+
+static void sgx_epc_misc_init(struct misc_cg *cg, struct sgx_epc_cgroup *epc_cg)
+{
+ cg->res[MISC_CG_RES_SGX_EPC].priv = epc_cg;
+ epc_cg->cg = cg;
+}
+
+static int sgx_epc_cgroup_alloc(struct misc_cg *cg)
+{
+ struct sgx_epc_cgroup *epc_cg;
+
+ epc_cg = kzalloc(sizeof(*epc_cg), GFP_KERNEL);
+ if (!epc_cg)
+ return -ENOMEM;
+
+ sgx_epc_misc_init(cg, epc_cg);
+
+ return 0;
+}
+
+void sgx_epc_cgroup_init(void)
+{
+ misc_cg_set_ops(MISC_CG_RES_SGX_EPC, &sgx_epc_cgroup_ops);
+ sgx_epc_misc_init(misc_cg_root(), &epc_cg_root);
+}
diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.h b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
new file mode 100644
index 000000000000..971df34f27d8
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2022 Intel Corporation. */
+#ifndef _INTEL_SGX_EPC_CGROUP_H_
+#define _INTEL_SGX_EPC_CGROUP_H_
+
+#include <asm/sgx.h>
+#include <linux/cgroup.h>
+#include <linux/list.h>
+#include <linux/misc_cgroup.h>
+#include <linux/page_counter.h>
+#include <linux/workqueue.h>
+
+#include "sgx.h"
+
+#ifndef CONFIG_CGROUP_SGX_EPC
+#define MISC_CG_RES_SGX_EPC MISC_CG_RES_TYPES
+struct sgx_epc_cgroup;
+
+static inline struct sgx_epc_cgroup *sgx_get_current_epc_cg(void)
+{
+ return NULL;
+}
+
+static inline void sgx_put_epc_cg(struct sgx_epc_cgroup *epc_cg) { }
+
+static inline int sgx_epc_cgroup_try_charge(struct sgx_epc_cgroup *epc_cg)
+{
+ return 0;
+}
+
+static inline void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg) { }
+
+static inline void sgx_epc_cgroup_init(void) { }
+#else
+struct sgx_epc_cgroup {
+ struct misc_cg *cg;
+};
+
+static inline struct sgx_epc_cgroup *sgx_epc_cgroup_from_misc_cg(struct misc_cg *cg)
+{
+ return (struct sgx_epc_cgroup *)(cg->res[MISC_CG_RES_SGX_EPC].priv);
+}
+
+/**
+ * sgx_get_current_epc_cg() - get the EPC cgroup of current process.
+ *
+ * Returned cgroup has its ref count increased by 1. Caller must call sgx_put_epc_cg()
+ * to return the reference.
+ *
+ * Return: EPC cgroup to which the current task belongs to.
+ */
+static inline struct sgx_epc_cgroup *sgx_get_current_epc_cg(void)
+{
+ return sgx_epc_cgroup_from_misc_cg(get_current_misc_cg());
+}
+
+/**
+ * sgx_put_epc_cg() - Put the EPC cgroup and reduce its ref count.
+ * @epc_cg - EPC cgroup to put.
+ */
+static inline void sgx_put_epc_cg(struct sgx_epc_cgroup *epc_cg)
+{
+ if (epc_cg)
+ put_misc_cg(epc_cg->cg);
+}
+
+int sgx_epc_cgroup_try_charge(struct sgx_epc_cgroup *epc_cg);
+void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg);
+void sgx_epc_cgroup_init(void);
+
+#endif
+
+#endif /* _INTEL_SGX_EPC_CGROUP_H_ */
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 166692f2d501..c32f18b70c73 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -6,6 +6,7 @@
#include <linux/highmem.h>
#include <linux/kthread.h>
#include <linux/miscdevice.h>
+#include <linux/misc_cgroup.h>
#include <linux/node.h>
#include <linux/pagemap.h>
#include <linux/ratelimit.h>
@@ -17,6 +18,7 @@
#include "driver.h"
#include "encl.h"
#include "encls.h"
+#include "epc_cgroup.h"

struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
static int sgx_nr_epc_sections;
@@ -558,7 +560,16 @@ int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
*/
struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
{
+ struct sgx_epc_cgroup *epc_cg;
struct sgx_epc_page *page;
+ int ret;
+
+ epc_cg = sgx_get_current_epc_cg();
+ ret = sgx_epc_cgroup_try_charge(epc_cg);
+ if (ret) {
+ sgx_put_epc_cg(epc_cg);
+ return ERR_PTR(ret);
+ }

for ( ; ; ) {
page = __sgx_alloc_epc_page();
@@ -567,8 +578,10 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
break;
}

- if (list_empty(&sgx_active_page_list))
- return ERR_PTR(-ENOMEM);
+ if (list_empty(&sgx_active_page_list)) {
+ page = ERR_PTR(-ENOMEM);
+ break;
+ }

if (!reclaim) {
page = ERR_PTR(-EBUSY);
@@ -580,10 +593,25 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
break;
}

+ /*
+ * Need to do a global reclamation if cgroup was not full but free
+ * physical pages run out, causing __sgx_alloc_epc_page() to fail.
+ */
sgx_reclaim_pages();
cond_resched();
}

+#ifdef CONFIG_CGROUP_SGX_EPC
+ if (!IS_ERR(page)) {
+ WARN_ON_ONCE(page->epc_cg);
+ /* sgx_put_epc_cg() in sgx_free_epc_page() */
+ page->epc_cg = epc_cg;
+ } else {
+ sgx_epc_cgroup_uncharge(epc_cg);
+ sgx_put_epc_cg(epc_cg);
+ }
+#endif
+
if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
wake_up(&ksgxd_waitq);

@@ -604,6 +632,14 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
struct sgx_epc_section *section = &sgx_epc_sections[page->section];
struct sgx_numa_node *node = section->node;

+#ifdef CONFIG_CGROUP_SGX_EPC
+ if (page->epc_cg) {
+ sgx_epc_cgroup_uncharge(page->epc_cg);
+ sgx_put_epc_cg(page->epc_cg);
+ page->epc_cg = NULL;
+ }
+#endif
+
spin_lock(&node->lock);

page->owner = NULL;
@@ -643,6 +679,11 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
section->pages[i].flags = 0;
section->pages[i].owner = NULL;
section->pages[i].poison = 0;
+
+#ifdef CONFIG_CGROUP_SGX_EPC
+ section->pages[i].epc_cg = NULL;
+#endif
+
list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
}

@@ -787,6 +828,7 @@ static void __init arch_update_sysfs_visibility(int nid) {}
static bool __init sgx_page_cache_init(void)
{
u32 eax, ebx, ecx, edx, type;
+ u64 capacity = 0;
u64 pa, size;
int nid;
int i;
@@ -837,6 +879,7 @@ static bool __init sgx_page_cache_init(void)

sgx_epc_sections[i].node = &sgx_numa_nodes[nid];
sgx_numa_nodes[nid].size += size;
+ capacity += size;

sgx_nr_epc_sections++;
}
@@ -846,6 +889,8 @@ static bool __init sgx_page_cache_init(void)
return false;
}

+ misc_cg_set_capacity(MISC_CG_RES_SGX_EPC, capacity);
+
return true;
}

@@ -942,6 +987,9 @@ static int __init sgx_init(void)
if (sgx_vepc_init() && ret)
goto err_provision;

+ /* Setup cgroup if either the native or vepc driver is active */
+ sgx_epc_cgroup_init();
+
return 0;

err_provision:
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index d2dad21259a8..a898d86dead0 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -29,12 +29,17 @@
/* Pages on free list */
#define SGX_EPC_PAGE_IS_FREE BIT(1)

+struct sgx_epc_cgroup;
+
struct sgx_epc_page {
unsigned int section;
u16 flags;
u16 poison;
struct sgx_encl_page *owner;
struct list_head list;
+#ifdef CONFIG_CGROUP_SGX_EPC
+ struct sgx_epc_cgroup *epc_cg;
+#endif
};

/*
diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
index 2f6cc3a0ad23..1a16efdfcd3d 100644
--- a/include/linux/misc_cgroup.h
+++ b/include/linux/misc_cgroup.h
@@ -46,11 +46,13 @@ struct misc_res_ops {
* @max: Maximum limit on the resource.
* @usage: Current usage of the resource.
* @events: Number of times, the resource limit exceeded.
+ * @priv: resource specific data.
*/
struct misc_res {
u64 max;
atomic64_t usage;
atomic64_t events;
+ void *priv;
};

/**
--
2.25.1