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Subject[RFC PATCH V2 17/22] x86/intel_rdt: Create character device exposing pseudo-locked region
Date
Once a pseudo-locked region has been created it needs to be made
available to user space to provide benefit there.

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_pseudo_lock.c | 267 +++++++++++++++++++++++++++-
1 file changed, 265 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index c03413021f45..b4923aa4314c 100644
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -26,6 +26,7 @@
#include <linux/kernfs.h>
#include <linux/kref.h>
#include <linux/kthread.h>
+#include <linux/mman.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/slab.h>
@@ -52,6 +53,14 @@
*/
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;
+
struct kernfs_node *pseudo_lock_kn;

/*
@@ -189,6 +198,15 @@ static void pseudo_lock_region_clear(struct pseudo_lock_region *plr)
plr->d = NULL;
}

+/**
+ * pseudo_lock_minor_release - Return minor number to available
+ * @minor: The minor number being released
+ */
+static void pseudo_lock_minor_release(unsigned int minor)
+{
+ __set_bit(minor, &pseudo_lock_minor_avail);
+}
+
static void __pseudo_lock_region_release(struct pseudo_lock_region *plr)
{
bool is_new_plr = (plr == new_plr);
@@ -199,6 +217,9 @@ static void __pseudo_lock_region_release(struct pseudo_lock_region *plr)

if (plr->locked) {
plr->d->plr = NULL;
+ device_destroy(pseudo_lock_class,
+ MKDEV(pseudo_lock_major, plr->minor));
+ pseudo_lock_minor_release(plr->minor);
/*
* Resource groups come and go. Simply returning this
* pseudo-locked region's bits to the default CLOS may
@@ -763,11 +784,74 @@ static int pseudo_lock_fn(void *_plr)
return 0;
}

+/**
+ * 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 allocated and returned.
+ *
+ * RETURNS:
+ * Zero on success, error 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;
+}
+
+/**
+ * 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.
+ *
+ * LOCKING:
+ * rdt_pseudo_lock_mutex must be held
+ *
+ * RETURNS:
+ * On success returns pointer to pseudo-locked region, NULL on failure.
+ */
+static struct pseudo_lock_region *region_find_by_minor(unsigned int minor)
+{
+ struct pseudo_lock_region *plr_match = NULL;
+ struct rdt_resource *r;
+ struct rdt_domain *d;
+
+ lockdep_assert_held(&rdt_pseudo_lock_mutex);
+
+ for_each_alloc_enabled_rdt_resource(r) {
+ list_for_each_entry(d, &r->domains, list) {
+ if (d->plr && d->plr->minor == minor) {
+ plr_match = d->plr;
+ break;
+ }
+ }
+ }
+ return plr_match;
+}
+
static int pseudo_lock_doit(struct pseudo_lock_region *plr,
struct rdt_resource *r,
struct rdt_domain *d)
{
struct task_struct *thread;
+ unsigned int new_minor;
+ struct device *dev;
int closid;
int ret, i;

@@ -858,11 +942,45 @@ static int pseudo_lock_doit(struct pseudo_lock_region *plr,
pseudo_lock_clos_set(plr, i, d->ctrl_val[0]);
}

+ ret = pseudo_lock_minor_get(&new_minor);
+ if (ret < 0) {
+ rdt_last_cmd_puts("unable to obtain a new minor number\n");
+ goto out_clos_def;
+ }
+
plr->locked = true;
d->plr = plr;
new_plr = NULL;

/*
+ * Unlock access but do not release the reference. The
+ * pseudo-locked region will still be here when we return.
+ * If anything else attempts to access the region while we do not
+ * have the mutex the region would be considered locked.
+ *
+ * We need to release the mutex 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 our mmap()
+ * callback is called.
+ */
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+
+ dev = device_create(pseudo_lock_class, NULL,
+ MKDEV(pseudo_lock_major, new_minor),
+ plr, "%s", plr->kn->name);
+
+ mutex_lock(&rdt_pseudo_lock_mutex);
+
+ if (IS_ERR(dev)) {
+ ret = PTR_ERR(dev);
+ rdt_last_cmd_printf("failed to created character device: %d\n",
+ ret);
+ goto out_minor;
+ }
+
+ plr->minor = new_minor;
+
+ /*
* We do not return CBM to CLOS here since that will result in a
* CBM of all zeroes which is an illegal MSR write.
*/
@@ -870,6 +988,8 @@ static int pseudo_lock_doit(struct pseudo_lock_region *plr,
ret = 0;
goto out;

+out_minor:
+ pseudo_lock_minor_release(new_minor);
out_clos_def:
pseudo_lock_clos_set(plr, 0, d->ctrl_val[0] | plr->cbm);
out_closid:
@@ -1184,6 +1304,127 @@ static int pseudo_lock_debugfs_create(void)
}
#endif

+static int pseudo_lock_dev_open(struct inode *inode, struct file *filp)
+{
+ struct pseudo_lock_region *plr;
+
+ mutex_lock(&rdt_pseudo_lock_mutex);
+
+ plr = region_find_by_minor(iminor(inode));
+ if (!plr) {
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+ return -ENODEV;
+ }
+
+ filp->private_data = plr;
+ /* Perform a non-seekable open - llseek is not supported */
+ filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
+
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+
+ return 0;
+}
+
+static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
+{
+ mutex_lock(&rdt_pseudo_lock_mutex);
+ filp->private_data = NULL;
+ mutex_unlock(&rdt_pseudo_lock_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 *file, 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;
+ unsigned long physical;
+ unsigned long psize;
+
+ mutex_lock(&rdt_pseudo_lock_mutex);
+
+ plr = file->private_data;
+ WARN_ON(!plr);
+ if (!plr) {
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+ return -ENODEV;
+ }
+
+ /*
+ * 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(&rdt_pseudo_lock_mutex);
+ return -EINVAL;
+ }
+
+ physical = __pa(plr->kmem) >> PAGE_SHIFT;
+ psize = plr->size - off;
+
+ if (off > plr->size) {
+ mutex_unlock(&rdt_pseudo_lock_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(&rdt_pseudo_lock_mutex);
+ return -EINVAL;
+ }
+
+ if (vsize > psize) {
+ mutex_unlock(&rdt_pseudo_lock_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(&rdt_pseudo_lock_mutex);
+ return -EAGAIN;
+ }
+ vma->vm_ops = &pseudo_mmap_ops;
+ mutex_unlock(&rdt_pseudo_lock_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 pseudo_lock_region *plr;
+
+ plr = dev_get_drvdata(dev);
+ if (mode)
+ *mode = 0600;
+ return kasprintf(GFP_KERNEL, "pseudo_lock/%s", plr->kn->name);
+}
+
/**
* rdt_pseudo_lock_fs_init - Create and initialize pseudo-locking files
* @root: location in kernfs where directory and files should be created
@@ -1245,10 +1486,26 @@ int rdt_pseudo_lock_fs_init(struct kernfs_node *root)
if (prefetch_disable_bits == 0)
return 0;

+ 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);
+ goto out_char;
+ }
+
+ pseudo_lock_class->devnode = pseudo_lock_devnode;
+
pseudo_lock_kn = kernfs_create_dir(root, "pseudo_lock",
root->mode, NULL);
- if (IS_ERR(pseudo_lock_kn))
- return PTR_ERR(pseudo_lock_kn);
+ if (IS_ERR(pseudo_lock_kn)) {
+ ret = PTR_ERR(pseudo_lock_kn);
+ goto out_class;
+ }

kn = __kernfs_create_file(pseudo_lock_kn, "avail", 0444,
0, &pseudo_lock_avail_ops,
@@ -1276,6 +1533,10 @@ int rdt_pseudo_lock_fs_init(struct kernfs_node *root)
error:
kernfs_remove(pseudo_lock_kn);
pseudo_lock_kn = NULL;
+out_class:
+ class_destroy(pseudo_lock_class);
+out_char:
+ unregister_chrdev(pseudo_lock_major, "pseudo_lock");
out:
return ret;
}
@@ -1321,5 +1582,7 @@ void rdt_pseudo_lock_fs_remove(void)
#endif
kernfs_remove(pseudo_lock_kn);
pseudo_lock_kn = NULL;
+ class_destroy(pseudo_lock_class);
+ unregister_chrdev(pseudo_lock_major, "pseudo_lock");
mutex_unlock(&rdt_pseudo_lock_mutex);
}
--
2.13.6
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