Re: [PATCH bpf-next 04/16] bpf: Introduce bpf_arena.

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On 2/8/24 01:26, Alexei Starovoitov wrote:
Also I believe I addressed all issues with missing mutex and wrap around,
and pushed to:
https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?h=arena&id=e1cb522fee661e7346e8be567eade9cf607eaf11
Please take a look.

LGTM, thanks.

minor things:

+static void arena_vm_close(struct vm_area_struct *vma)
+{
+	struct vma_list *vml;
+
+	vml = vma->vm_private_data;
+	list_del(&vml->head);
+	vma->vm_private_data = NULL;
+	kfree(vml);
+}

i think this also needs protected by the arena mutex. otherwise two VMAs that close at the same time can corrupt the arena vma_list. or a VMA that closes while you're zapping.

remember_vma() already has the mutex held, since it's called from mmap.

+static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt, int node_id)
+{
+	long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT;

this function and arena_free_pages() are both using user_vm_start/end before grabbing the mutex. so need to grab the mutex very early.

alternatively, you could make it so that the user must set the user_vm_start via map_extra, so you don't have to worry about these changing after the arena is created.

thanks,

barret







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