On 3/30/22 14:25, Claudio Imbrenda wrote:
Refactor s390_reset_acc so that it can be reused in upcoming patches.
We don't want to hold all the locks used in a walk_page_range for too
long, and the destroy page UVC does take some time to complete.
Therefore we quickly gather the pages to destroy, and then destroy them
without holding all the locks.
The new refactored function optionally allows to return early without
completing if a fatal signal is pending (and return and appropriate
error code). Two wrappers are provided to call the new function.
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
(dropping Janosch's Ack because of major changes to the patch)
Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
[...]
+#define DESTROY_LOOP_THRESHOLD 32
A question out of curiosity:
Is there any particular reason for the number?
Have you tested other numbers and experienced a speedup/slowdown?
+
+struct reset_walk_state {
+ unsigned long next;
+ unsigned long count;
+ unsigned long pfns[DESTROY_LOOP_THRESHOLD];
+};
+
+static int s390_gather_pages(pte_t *ptep, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
{
+ struct reset_walk_state *p = walk->private;
pte_t pte = READ_ONCE(*ptep);
- /* There is a reference through the mapping */
- if (pte_present(pte))
- WARN_ON_ONCE(uv_destroy_owned_page(pte_val(pte) & PAGE_MASK));
-
- return 0;
+ if (pte_present(pte)) {
+ /* we have a reference from the mapping, take an extra one */
+ get_page(phys_to_page(pte_val(pte)));
+ p->pfns[p->count] = phys_to_pfn(pte_val(pte));
+ p->next = next;
+ p->count++;
+ }
+ return p->count >= DESTROY_LOOP_THRESHOLD;
}
-static const struct mm_walk_ops reset_acc_walk_ops = {
- .pte_entry = __s390_reset_acc,
+static const struct mm_walk_ops gather_pages_ops = {
+ .pte_entry = s390_gather_pages,
};
-#include <linux/sched/mm.h>
-void s390_reset_acc(struct mm_struct *mm)
+/*
+ * Call the Destroy secure page UVC on each page in the given array of PFNs.
+ * Each page needs to have an extra reference, which will be released here.
+ */
+void s390_uv_destroy_pfns(unsigned long count, unsigned long *pfns)
{
- if (!mm_is_protected(mm))
- return;
- /*
- * we might be called during
- * reset: we walk the pages and clear
- * close of all kvm file descriptors: we walk the pages and clear
- * exit of process on fd closure: vma already gone, do nothing
- */
- if (!mmget_not_zero(mm))
- return;
- mmap_read_lock(mm);
- walk_page_range(mm, 0, TASK_SIZE, &reset_acc_walk_ops, NULL);
- mmap_read_unlock(mm);
- mmput(mm);
+ unsigned long i;
+
+ for (i = 0; i < count; i++) {
+ /* we always have an extra reference */
+ uv_destroy_owned_page(pfn_to_phys(pfns[i]));
+ /* get rid of the extra reference */
+ put_page(pfn_to_page(pfns[i]));
+ cond_resched();
+ }
+}
+EXPORT_SYMBOL_GPL(s390_uv_destroy_pfns);
+
+/**
+ * __s390_uv_destroy_range - Walk the given range of the given address
+ * space, and call the destroy secure page UVC on each page.
+ * Optionally exit early if a fatal signal is pending.
+ * @mm the mm to operate on
+ * @start the start of the range
+ * @end the end of the range
+ * @interruptible if not 0, stop when a fatal signal is received
+ * Return: 0 on success, -EINTR if the function stopped before completing
+ */
+int __s390_uv_destroy_range(struct mm_struct *mm, unsigned long start,
+ unsigned long end, bool interruptible)
+{
+ struct reset_walk_state state = { .next = start };
+ int r = 1;
+
+ while (r > 0) {
+ state.count = 0;
+ mmap_read_lock(mm);
+ r = walk_page_range(mm, state.next, end, &gather_pages_ops, &state);
+ mmap_read_unlock(mm);
+ cond_resched();
+ s390_uv_destroy_pfns(state.count, state.pfns);
+ if (interruptible && fatal_signal_pending(current))
+ return -EINTR;
+ }
+ return 0;
}
-EXPORT_SYMBOL_GPL(s390_reset_acc);
+EXPORT_SYMBOL_GPL(__s390_uv_destroy_range);
/**
* s390_remove_old_asce - Remove the topmost level of page tables from the
