[PATCH 12/16] mm: update resctl to use mmap_prepare, mmap_complete, mmap_abort

Lorenzo Stoakes
2025-09-08T11:12:27Z

resctl uses remap_pfn_range(), but holds a mutex over the
operation. Therefore, establish the mutex in mmap_prepare(), release it in
mmap_complete() and release it in mmap_abort() should the operation fail.

Otherwise, we simply make use of the remap_pfn_range_[prepare/complete]()
remap PFN range variants in an ordinary way.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
fs/resctrl/pseudo_lock.c | 56 +++++++++++++++++++++++++++++++---------
1 file changed, 44 insertions(+), 12 deletions(-)

diff --git a/fs/resctrl/pseudo_lock.c b/fs/resctrl/pseudo_lock.c
index 87bbc2605de1..6d18ffde6a94 100644
--- a/fs/resctrl/pseudo_lock.c
+++ b/fs/resctrl/pseudo_lock.c
@@ -995,7 +995,8 @@ 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)
+static int pseudo_lock_dev_mmap_complete(struct file *filp, struct vm_area_struct *vma,
+ const void *context)
{
unsigned long vsize = vma->vm_end - vma->vm_start;
unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
@@ -1004,6 +1005,40 @@ static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
unsigned long physical;
unsigned long psize;

+ rdtgrp = filp->private_data;
+ plr = rdtgrp->plr;
+
+ physical = __pa(plr->kmem) >> PAGE_SHIFT;
+ psize = plr->size - off;
+
+ memset(plr->kmem + off, 0, vsize);
+
+ if (remap_pfn_range_complete(vma, vma->vm_start, physical + vma->vm_pgoff,
+ vsize, vma->vm_page_prot)) {
+ mutex_unlock(&rdtgroup_mutex);
+ return -EAGAIN;
+ }
+
+ mutex_unlock(&rdtgroup_mutex);
+ return 0;
+}
+
+static void pseudo_lock_dev_mmap_abort(const struct file *filp,
+ const void *vm_private_data,
+ const void *context)
+{
+ mutex_unlock(&rdtgroup_mutex);
+}
+
+static int pseudo_lock_dev_mmap_prepare(struct vm_area_desc *desc)
+{
+ unsigned long vsize = vma_desc_size(desc);
+ unsigned long off = desc->pgoff << PAGE_SHIFT;
+ struct file *filp = desc->file;
+ struct pseudo_lock_region *plr;
+ struct rdtgroup *rdtgrp;
+ unsigned long psize;
+
mutex_lock(&rdtgroup_mutex);

rdtgrp = filp->private_data;
@@ -1031,7 +1066,6 @@ static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
return -EINVAL;
}

- physical = __pa(plr->kmem) >> PAGE_SHIFT;
psize = plr->size - off;

if (off > plr->size) {
@@ -1043,7 +1077,7 @@ static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
* Ensure changes are carried directly to the memory being mapped,
* do not allow copy-on-write mapping.
*/
- if (!(vma->vm_flags & VM_SHARED)) {
+ if (!(desc->vm_flags & VM_SHARED)) {
mutex_unlock(&rdtgroup_mutex);
return -EINVAL;
}
@@ -1053,15 +1087,11 @@ static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
return -ENOSPC;
}

- memset(plr->kmem + off, 0, vsize);
+ /* No CoW allowed so don't need to specify pfn. */
+ remap_pfn_range_prepare(desc, 0);
+ desc->vm_ops = &pseudo_mmap_ops;

- 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);
+ /* mutex will be release in mmap_complete or mmap_abort. */
return 0;
}

@@ -1071,7 +1101,9 @@ static const struct file_operations pseudo_lock_dev_fops = {
.write = NULL,
.open = pseudo_lock_dev_open,
.release = pseudo_lock_dev_release,
- .mmap = pseudo_lock_dev_mmap,
+ .mmap_prepare = pseudo_lock_dev_mmap_prepare,
+ .mmap_complete = pseudo_lock_dev_mmap_complete,
+ .mmap_abort = pseudo_lock_dev_mmap_abort,
};

int rdt_pseudo_lock_init(void)
--
2.51.0