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Message-ID: <4d681184-c285-4d79-8e5f-f4b3f23c9f25@lucifer.local>
Date: Wed, 13 Aug 2025 07:10:43 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tglx@...utronix.de, linux-kernel@...r.kernel.org,
torvalds@...uxfoundation.org, mingo@...nel.org, namhyung@...nel.org,
acme@...hat.com, kees@...nel.org
Subject: Re: [PATCH v3 10/15] perf: Split out the AUX buffer allocation
On Tue, Aug 12, 2025 at 12:39:08PM +0200, Peter Zijlstra wrote:
> Move the AUX buffer allocation branch into its own function.
>
> Originally-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
LGTM (one nitty note below :), so:
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
> kernel/events/core.c | 144 +++++++++++++++++++++++++++------------------------
> 1 file changed, 77 insertions(+), 67 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6970,6 +6970,82 @@ static void perf_mmap_account(struct vm_
> atomic64_add(extra, &vma->vm_mm->pinned_vm);
> }
>
> +static int perf_mmap_aux(struct vm_area_struct *vma, struct perf_event *event,
> + unsigned long nr_pages)
> +{
> + long extra = 0, user_extra = nr_pages;
> + u64 aux_offset, aux_size;
> + struct perf_buffer *rb;
> + int ret, rb_flags = 0;
> +
> + rb = event->rb;
> + if (!rb)
> + return -EINVAL;
> +
> + guard(mutex)(&rb->aux_mutex);
> +
> + /*
> + * AUX area mapping: if rb->aux_nr_pages != 0, it's already
> + * mapped, all subsequent mappings should have the same size
> + * and offset. Must be above the normal perf buffer.
> + */
> + aux_offset = READ_ONCE(rb->user_page->aux_offset);
> + aux_size = READ_ONCE(rb->user_page->aux_size);
> +
> + if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
> + return -EINVAL;
> +
> + if (aux_offset != vma->vm_pgoff << PAGE_SHIFT)
> + return -EINVAL;
> +
> + /* already mapped with a different offset */
> + if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
> + return -EINVAL;
> +
> + if (aux_size != nr_pages * PAGE_SIZE)
> + return -EINVAL;
> +
> + /* already mapped with a different size */
> + if (rb_has_aux(rb) && rb->aux_nr_pages != nr_pages)
> + return -EINVAL;
> +
> + if (!is_power_of_2(nr_pages))
> + return -EINVAL;
> +
> + if (!atomic_inc_not_zero(&rb->mmap_count))
> + return -EINVAL;
> +
> + if (rb_has_aux(rb)) {
> + atomic_inc(&rb->aux_mmap_count);
> +
Still that extra line :>)
> + } else {
> + if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
> + atomic_dec(&rb->mmap_count);
> + return -EPERM;
> + }
> +
> + WARN_ON(!rb && event->rb);
> +
> + if (vma->vm_flags & VM_WRITE)
> + rb_flags |= RING_BUFFER_WRITABLE;
> +
> + ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
> + event->attr.aux_watermark, rb_flags);
> + if (ret) {
> + atomic_dec(&rb->mmap_count);
> + return ret;
> + }
> +
> + atomic_set(&rb->aux_mmap_count, 1);
> + rb->aux_mmap_locked = extra;
> + }
> +
> + perf_mmap_account(vma, user_extra, extra);
> + atomic_inc(&event->mmap_count);
> +
> + return 0;
> +}
> +
> static int perf_mmap(struct file *file, struct vm_area_struct *vma)
> {
> struct perf_event *event = file->private_data;
> @@ -7087,73 +7163,7 @@ static int perf_mmap(struct file *file,
> perf_mmap_account(vma, user_extra, extra);
> atomic_inc(&event->mmap_count);
> } else {
> - /*
> - * AUX area mapping: if rb->aux_nr_pages != 0, it's already
> - * mapped, all subsequent mappings should have the same size
> - * and offset. Must be above the normal perf buffer.
> - */
> - u64 aux_offset, aux_size;
> -
> - rb = event->rb;
> - if (!rb)
> - goto unlock;
> -
> - guard(mutex)(&rb->aux_mutex);
> -
> - aux_offset = READ_ONCE(rb->user_page->aux_offset);
> - aux_size = READ_ONCE(rb->user_page->aux_size);
> -
> - if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
> - goto unlock;
> -
> - if (aux_offset != vma->vm_pgoff << PAGE_SHIFT)
> - goto unlock;
> -
> - /* already mapped with a different offset */
> - if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
> - goto unlock;
> -
> - if (aux_size != nr_pages * PAGE_SIZE)
> - goto unlock;
> -
> - /* already mapped with a different size */
> - if (rb_has_aux(rb) && rb->aux_nr_pages != nr_pages)
> - goto unlock;
> -
> - if (!is_power_of_2(nr_pages))
> - goto unlock;
> -
> - if (!atomic_inc_not_zero(&rb->mmap_count))
> - goto unlock;
> -
> - if (rb_has_aux(rb)) {
> - atomic_inc(&rb->aux_mmap_count);
> - ret = 0;
> -
> - } else {
> - if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
> - ret = -EPERM;
> - atomic_dec(&rb->mmap_count);
> - goto unlock;
> - }
> -
> - WARN_ON(!rb && event->rb);
> -
> - if (vma->vm_flags & VM_WRITE)
> - flags |= RING_BUFFER_WRITABLE;
> -
> - ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
> - event->attr.aux_watermark, flags);
> - if (ret) {
> - atomic_dec(&rb->mmap_count);
> - goto unlock;
> - }
> -
> - atomic_set(&rb->aux_mmap_count, 1);
> - rb->aux_mmap_locked = extra;
> - }
> - perf_mmap_account(vma, user_extra, extra);
> - atomic_inc(&event->mmap_count);
> + ret = perf_mmap_aux(vma, event, nr_pages);
> }
>
> unlock:
>
>
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