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Subject[PATCH V3 35/39] x86/intel_rdt: Create character device exposing pseudo-locked region
Date
After a pseudo-locked region is created it needs to be made
available to user space for usage.

A character device supporting mmap() is created for each pseudo-locked
region. A user space application can now use mmap() system call to map
pseudo-locked region into its virtual address space.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
arch/x86/kernel/cpu/intel_rdt.h | 5 +
arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c | 282 +++++++++++++++++++++++++++-
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 11 +-
3 files changed, 296 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index be62c39e18f6..db3aa956cd1c 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -137,6 +137,8 @@ struct mongroup {
* @line_size: size of the cache lines
* @size: size of pseudo-locked region in bytes
* @kmem: the kernel memory associated with pseudo-locked region
+ * @minor: minor number of character device associated with this
+ * region
* @debugfs_dir: pointer to this region's directory in the debugfs
* filesystem
*/
@@ -150,6 +152,7 @@ struct pseudo_lock_region {
unsigned int line_size;
unsigned int size;
void *kmem;
+ unsigned int minor;
#ifdef CONFIG_INTEL_RDT_DEBUGFS
struct dentry *debugfs_dir;
#endif
@@ -513,6 +516,8 @@ int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp);
bool rdtgroup_cbm_overlaps_pseudo_locked(struct rdt_domain *d, u32 _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);
diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index 8a52e5e61f3e..cc51a2c653bb 100644
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -24,6 +24,7 @@
#include <linux/cpumask.h>
#include <linux/debugfs.h>
#include <linux/kthread.h>
+#include <linux/mman.h>
#include <linux/slab.h>
#include <asm/cacheflush.h>
#include <asm/intel-family.h>
@@ -48,6 +49,14 @@
*/
static u64 prefetch_disable_bits;

+/*
+ * Major number assigned to and shared by all devices exposing
+ * pseudo-locked regions.
+ */
+static unsigned int pseudo_lock_major;
+static unsigned long pseudo_lock_minor_avail = GENMASK(MINORBITS, 0);
+static struct class *pseudo_lock_class;
+
/**
* get_prefetch_disable_bits - prefetch disable bits of supported platforms
*
@@ -100,6 +109,66 @@ static u64 get_prefetch_disable_bits(void)
}

/**
+ * pseudo_lock_minor_get - Obtain available minor number
+ * @minor: Pointer to where new minor number will be stored
+ *
+ * A bitmask is used to track available minor numbers. Here the next free
+ * minor number is marked as unavailable and returned.
+ *
+ * Return: 0 on success, <0 on failure.
+ */
+static int pseudo_lock_minor_get(unsigned int *minor)
+{
+ unsigned long first_bit;
+
+ first_bit = find_first_bit(&pseudo_lock_minor_avail, MINORBITS);
+
+ if (first_bit == MINORBITS)
+ return -ENOSPC;
+
+ __clear_bit(first_bit, &pseudo_lock_minor_avail);
+ *minor = first_bit;
+
+ return 0;
+}
+
+/**
+ * pseudo_lock_minor_release - Return minor number to available
+ * @minor: The minor number made available
+ */
+static void pseudo_lock_minor_release(unsigned int minor)
+{
+ __set_bit(minor, &pseudo_lock_minor_avail);
+}
+
+/**
+ * region_find_by_minor - Locate a pseudo-lock region by inode minor number
+ * @minor: The minor number of the device representing pseudo-locked region
+ *
+ * When the character device is accessed we need to determine which
+ * pseudo-locked region it belongs to. This is done by matching the minor
+ * number of the device to the pseudo-locked region it belongs.
+ *
+ * Minor numbers are assigned at the time a pseudo-locked region is associated
+ * with a cache instance.
+ *
+ * Return: On success return pointer to resource group owning the pseudo-locked
+ * region, NULL on failure.
+ */
+static struct rdtgroup *region_find_by_minor(unsigned int minor)
+{
+ struct rdtgroup *rdtgrp, *rdtgrp_match = NULL;
+
+ list_for_each_entry(rdtgrp, &rdt_all_groups, rdtgroup_list) {
+ if (rdtgrp->plr && rdtgrp->plr->minor == minor) {
+ rdtgrp_match = rdtgrp;
+ break;
+ }
+ }
+ return rdtgrp_match;
+}
+
+/**
* pseudo_lock_region_init - Initialize pseudo-lock region information
* @plr: pseudo-lock region
*
@@ -866,9 +935,11 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
{
struct pseudo_lock_region *plr = rdtgrp->plr;
struct task_struct *thread;
+ unsigned int new_minor;
#ifdef CONFIG_INTEL_RDT_DEBUGFS
struct dentry *entry;
#endif
+ struct device *dev;
int ret;

ret = pseudo_lock_region_alloc(plr);
@@ -922,13 +993,55 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
}
#endif

+ ret = pseudo_lock_minor_get(&new_minor);
+ if (ret < 0) {
+ rdt_last_cmd_puts("unable to obtain a new minor number\n");
+ goto out_debugfs;
+ }
+
+ /*
+ * Unlock access but do not release the reference. The
+ * pseudo-locked region will still be here on return.
+ *
+ * The mutex has to be released temporarily to avoid a potential
+ * deadlock with the mm->mmap_sem semaphore which is obtained in
+ * the device_create() callpath below as well as before the mmap()
+ * callback is called.
+ */
+ mutex_unlock(&rdtgroup_mutex);
+
+ dev = device_create(pseudo_lock_class, NULL,
+ MKDEV(pseudo_lock_major, new_minor),
+ rdtgrp, "%s", rdtgrp->kn->name);
+
+ mutex_lock(&rdtgroup_mutex);
+
+ if (IS_ERR(dev)) {
+ ret = PTR_ERR(dev);
+ rdt_last_cmd_printf("failed to create character device: %d\n",
+ ret);
+ goto out_minor;
+ }
+
+ /* We released the mutex - check if group was removed while we did so */
+ if (rdtgrp->flags & RDT_DELETED) {
+ ret = -ENODEV;
+ goto out_device;
+ }
+
+ plr->minor = new_minor;
+
rdtgrp->mode = RDT_MODE_PSEUDO_LOCKED;
closid_free(rdtgrp->closid);
ret = 0;
goto out;

-#ifdef CONFIG_INTEL_RDT_DEBUGFS
+out_device:
+ device_destroy(pseudo_lock_class, MKDEV(pseudo_lock_major, new_minor));
+out_minor:
+ pseudo_lock_minor_release(new_minor);
out_debugfs:
+#ifdef CONFIG_INTEL_RDT_DEBUGFS
debugfs_remove_recursive(plr->debugfs_dir);
#endif
out_region:
@@ -953,6 +1066,8 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
*/
void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp)
{
+ struct pseudo_lock_region *plr = rdtgrp->plr;
+
if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
/*
* Default group cannot be a pseudo-locked region so we can
@@ -965,7 +1080,172 @@ void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp)
#ifdef CONFIG_INTEL_RDT_DEBUGFS
debugfs_remove_recursive(rdtgrp->plr->debugfs_dir);
#endif
+ device_destroy(pseudo_lock_class, MKDEV(pseudo_lock_major, plr->minor));
+ pseudo_lock_minor_release(plr->minor);

free:
pseudo_lock_free(rdtgrp);
}
+
+static int pseudo_lock_dev_open(struct inode *inode, struct file *filp)
+{
+ struct rdtgroup *rdtgrp;
+
+ mutex_lock(&rdtgroup_mutex);
+
+ rdtgrp = region_find_by_minor(iminor(inode));
+ if (!rdtgrp) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -ENODEV;
+ }
+
+ filp->private_data = rdtgrp;
+ atomic_inc(&rdtgrp->waitcount);
+ /* Perform a non-seekable open - llseek is not supported */
+ filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
+
+ mutex_unlock(&rdtgroup_mutex);
+
+ return 0;
+}
+
+static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
+{
+ struct rdtgroup *rdtgrp;
+
+ mutex_lock(&rdtgroup_mutex);
+ rdtgrp = filp->private_data;
+ WARN_ON(!rdtgrp);
+ if (!rdtgrp) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -ENODEV;
+ }
+ filp->private_data = NULL;
+ atomic_dec(&rdtgrp->waitcount);
+ mutex_unlock(&rdtgroup_mutex);
+ return 0;
+}
+
+static int pseudo_lock_dev_mremap(struct vm_area_struct *area)
+{
+ /* Not supported */
+ return -EINVAL;
+}
+
+static const struct vm_operations_struct pseudo_mmap_ops = {
+ .mremap = pseudo_lock_dev_mremap,
+};
+
+static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ unsigned long vsize = vma->vm_end - vma->vm_start;
+ unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
+ struct pseudo_lock_region *plr;
+ struct rdtgroup *rdtgrp;
+ unsigned long physical;
+ unsigned long psize;
+
+ mutex_lock(&rdtgroup_mutex);
+
+ rdtgrp = filp->private_data;
+ WARN_ON(!rdtgrp);
+ if (!rdtgrp) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -ENODEV;
+ }
+
+ plr = rdtgrp->plr;
+
+ /*
+ * Task is required to run with affinity to the cpus associated
+ * with the pseudo-locked region. If this is not the case the task
+ * may be scheduled elsewhere and invalidate entries in the
+ * pseudo-locked region.
+ */
+ if (!cpumask_subset(&current->cpus_allowed, &plr->d->cpu_mask)) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -EINVAL;
+ }
+
+ physical = __pa(plr->kmem) >> PAGE_SHIFT;
+ psize = plr->size - off;
+
+ if (off > plr->size) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -ENOSPC;
+ }
+
+ /*
+ * Ensure changes are carried directly to the memory being mapped,
+ * do not allow copy-on-write mapping.
+ */
+ if (!(vma->vm_flags & VM_SHARED)) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -EINVAL;
+ }
+
+ if (vsize > psize) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -ENOSPC;
+ }
+
+ memset(plr->kmem + off, 0, vsize);
+
+ if (remap_pfn_range(vma, vma->vm_start, physical + vma->vm_pgoff,
+ vsize, vma->vm_page_prot)) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -EAGAIN;
+ }
+ vma->vm_ops = &pseudo_mmap_ops;
+ mutex_unlock(&rdtgroup_mutex);
+ return 0;
+}
+
+static const struct file_operations pseudo_lock_dev_fops = {
+ .owner = THIS_MODULE,
+ .llseek = no_llseek,
+ .read = NULL,
+ .write = NULL,
+ .open = pseudo_lock_dev_open,
+ .release = pseudo_lock_dev_release,
+ .mmap = pseudo_lock_dev_mmap,
+};
+
+static char *pseudo_lock_devnode(struct device *dev, umode_t *mode)
+{
+ struct rdtgroup *rdtgrp;
+
+ rdtgrp = dev_get_drvdata(dev);
+ if (mode)
+ *mode = 0600;
+ return kasprintf(GFP_KERNEL, "pseudo_lock/%s", rdtgrp->kn->name);
+}
+
+int rdt_pseudo_lock_init(void)
+{
+ int ret;
+
+ ret = register_chrdev(0, "pseudo_lock", &pseudo_lock_dev_fops);
+ if (ret < 0)
+ return ret;
+
+ pseudo_lock_major = ret;
+
+ pseudo_lock_class = class_create(THIS_MODULE, "pseudo_lock");
+ if (IS_ERR(pseudo_lock_class)) {
+ ret = PTR_ERR(pseudo_lock_class);
+ unregister_chrdev(pseudo_lock_major, "pseudo_lock");
+ return ret;
+ }
+
+ pseudo_lock_class->devnode = pseudo_lock_devnode;
+ return 0;
+}
+
+void rdt_pseudo_lock_release(void)
+{
+ class_destroy(pseudo_lock_class);
+ pseudo_lock_class = NULL;
+ unregister_chrdev(pseudo_lock_major, "pseudo_lock");
+ pseudo_lock_major = 0;
+}
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 0d8dbe11b8dd..a38ddfe7d552 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -1831,10 +1831,16 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
rdtgroup_default.mon.mon_data_kn = kn_mondata;
}

+ ret = rdt_pseudo_lock_init();
+ if (ret) {
+ dentry = ERR_PTR(ret);
+ goto out_mondata;
+ }
+
dentry = kernfs_mount(fs_type, flags, rdt_root,
RDTGROUP_SUPER_MAGIC, NULL);
if (IS_ERR(dentry))
- goto out_mondata;
+ goto out_psl;

if (rdt_alloc_capable)
static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
@@ -1852,6 +1858,8 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,

goto out;

+out_psl:
+ rdt_pseudo_lock_release();
out_mondata:
if (rdt_mon_capable)
kernfs_remove(kn_mondata);
@@ -2027,6 +2035,7 @@ static void rdt_kill_sb(struct super_block *sb)
reset_all_ctrls(r);
cdp_disable_all();
rmdir_all_sub();
+ rdt_pseudo_lock_release();
rdtgroup_default.mode = RDT_MODE_SHAREABLE;
static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
static_branch_disable_cpuslocked(&rdt_mon_enable_key);
--
2.13.6
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