[PATCH v6 04/12] x86/sgx: Implement basic EPC misc cgroup functionality

Haitao Huang
2023-10-30T18:20:46Z

From: Kristen Carlson Accardi <kristen@linux.intel.com>

Implement support for cgroup control of SGX Enclave Page Cache (EPC)
memory using the misc cgroup controller. EPC memory is independent
from normal system memory, e.g. must be reserved at boot from RAM and
cannot be converted between EPC and normal memory while the system is
running. EPC is managed by the SGX subsystem and is not accounted by
the memory controller.

Much like normal system memory, EPC memory can be overcommitted via
virtual memory techniques and pages can be swapped out of the EPC to
their backing store (normal system memory, e.g. shmem). The SGX EPC
subsystem is analogous to the memory subsystem and the SGX EPC controller
is in turn analogous to the memory controller; it implements limit and
protection models for EPC memory.

The misc controller provides a mechanism to set a hard limit of EPC
usage via the "sgx_epc" resource in "misc.max". The total EPC memory
available on the system is reported via the "sgx_epc" resource in
"misc.capacity".

This patch was modified from the previous version to only add basic EPC
cgroup structure, accounting allocations for cgroup usage
(charge/uncharge), setup misc cgroup callbacks, set total EPC capacity.

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
globale reclaimer and implement per-cgroup tracking and reclaiming.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
---
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 | 103 +++++++++++++++++++++++++++
arch/x86/kernel/cpu/sgx/epc_cgroup.h | 36 ++++++++++
arch/x86/kernel/cpu/sgx/main.c | 28 ++++++++
arch/x86/kernel/cpu/sgx/sgx.h | 3 +
6 files changed, 184 insertions(+)
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 66bfabae8814..e17c5dc3aea4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1921,6 +1921,19 @@ 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..500627d0563f
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright(c) 2022 Intel Corporation.
+
+#include <linux/atomic.h>
+#include <linux/kernel.h>
+#include "epc_cgroup.h"
+
+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);
+}
+
+static inline bool sgx_epc_cgroup_disabled(void)
+{
+ return !cgroup_subsys_enabled(misc_cgrp_subsys);
+}
+
+/**
+ * sgx_epc_cgroup_try_charge() - hierarchically try to charge a single EPC page
+ *
+ * Returns EPC cgroup or NULL on success, -errno on failure.
+ */
+struct sgx_epc_cgroup *sgx_epc_cgroup_try_charge(void)
+{
+ struct sgx_epc_cgroup *epc_cg;
+ int ret;
+
+ if (sgx_epc_cgroup_disabled())
+ return NULL;
+
+ epc_cg = sgx_epc_cgroup_from_misc_cg(get_current_misc_cg());
+ ret = misc_cg_try_charge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE);
+
+ if (!ret) {
+ /* No epc_cg returned, release ref from get_current_misc_cg() */
+ put_misc_cg(epc_cg->cg);
+ return ERR_PTR(-ENOMEM);
+ }
+
+ /* Ref released in sgx_epc_cgroup_uncharge() */
+ return epc_cg;
+}
+
+/**
+ * sgx_epc_cgroup_uncharge() - hierarchically uncharge EPC pages
+ * @epc_cg: the charged epc cgroup
+ */
+void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg)
+{
+ if (sgx_epc_cgroup_disabled())
+ return;
+
+ misc_cg_uncharge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE);
+
+ /* Ref got from sgx_epc_cgroup_try_charge() */
+ put_misc_cg(epc_cg->cg);
+}
+
+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_operations_struct sgx_epc_cgroup_ops = {
+ .alloc = sgx_epc_cgroup_alloc,
+ .free = sgx_epc_cgroup_free,
+};
+
+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;
+
+ cg->res[MISC_CG_RES_SGX_EPC].misc_ops = &sgx_epc_cgroup_ops;
+ cg->res[MISC_CG_RES_SGX_EPC].priv = epc_cg;
+ epc_cg->cg = cg;
+ return 0;
+}
+
+static int __init sgx_epc_cgroup_init(void)
+{
+ struct misc_cg *cg;
+
+ if (!boot_cpu_has(X86_FEATURE_SGX))
+ return 0;
+
+ cg = misc_cg_root();
+ BUG_ON(!cg);
+
+ return sgx_epc_cgroup_alloc(cg);
+}
+subsys_initcall(sgx_epc_cgroup_init);
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..c3abfe82be15
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -0,0 +1,36 @@
+/* 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_epc_cgroup_try_charge(void)
+{
+ return NULL;
+}
+
+static inline void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg) { }
+#else
+struct sgx_epc_cgroup {
+ struct misc_cg *cg;
+};
+
+struct sgx_epc_cgroup *sgx_epc_cgroup_try_charge(void);
+void sgx_epc_cgroup_uncharge(struct sgx_epc_cgroup *epc_cg);
+bool sgx_epc_cgroup_lru_empty(struct misc_cg *root);
+
+#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..07606f391540 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;
@@ -559,6 +561,11 @@ 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_page *page;
+ struct sgx_epc_cgroup *epc_cg;
+
+ epc_cg = sgx_epc_cgroup_try_charge();
+ if (IS_ERR(epc_cg))
+ return ERR_CAST(epc_cg);

for ( ; ; ) {
page = __sgx_alloc_epc_page();
@@ -580,10 +587,21 @@ 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();
}

+ if (!IS_ERR(page)) {
+ WARN_ON_ONCE(page->epc_cg);
+ page->epc_cg = epc_cg;
+ } else {
+ sgx_epc_cgroup_uncharge(epc_cg);
+ }
+
if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
wake_up(&ksgxd_waitq);

@@ -604,6 +622,11 @@ 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;

+ if (page->epc_cg) {
+ sgx_epc_cgroup_uncharge(page->epc_cg);
+ page->epc_cg = NULL;
+ }
+
spin_lock(&node->lock);

page->owner = NULL;
@@ -643,6 +666,7 @@ 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;
+ section->pages[i].epc_cg = NULL;
list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
}

@@ -787,6 +811,7 @@ 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 +862,7 @@ 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 +872,8 @@ static bool __init sgx_page_cache_init(void)
return false;
}

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

diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index d2dad21259a8..b1786774b8d2 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -29,12 +29,15 @@
/* 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;
+ struct sgx_epc_cgroup *epc_cg;
};

/*
--
2.25.1