Messages in this thread | | | Date | Thu, 31 Mar 2022 15:25:31 +0200 | Subject | Re: [PATCH v9 04/18] KVM: s390: pv: refactor s390_reset_acc | From | Janosch Frank <> |
| |
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@linux.ibm.com> > (dropping Janosch's Ack because of major changes to the patch)
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
[...] > +#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
| |