>>>> +/* Pgoff for mmaping the rings */
>>>> +#define XDP_UMEM_PGOFF_FILL_RING 0x100000000
>>>> +
>>>> +struct xdp_ring {
>>>> + __u32 producer __attribute__((aligned(64)));
>>>> + __u32 consumer __attribute__((aligned(64)));
>>>> +};
>>>
>>> Why 64? And do you still need these guys in uapi?
>>
>> I was just about to ask the same. You mean cacheline_aligned?
>
> Yes, I would like to have these cache aligned. How can I accomplish
> this in a uapi?
Good point. This seems fine to me.
> I put a note around this in the cover letter:
>
> * How to deal with cache alignment for uapi when different
> architectures can have different cache line sizes? We have just
> aligned it to 64 bytes for now, which works for many popular
> architectures, but not all. Please advise.
>
>>
>>>> +static int xsk_mmap(struct file *file, struct socket *sock,
>>>> + struct vm_area_struct *vma)
>>>> +{
>>>> + unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
>>>> + unsigned long size = vma->vm_end - vma->vm_start;
>>>> + struct xdp_sock *xs = xdp_sk(sock->sk);
>>>> + struct xsk_queue *q;
>>>> + unsigned long pfn;
>>>> + struct page *qpg;
>>>> +
>>>> + if (!xs->umem)
>>>> + return -EINVAL;
>>>> +
>>>> + if (offset == XDP_UMEM_PGOFF_FILL_RING)
>>>> + q = xs->umem->fq;
>>>> + else
>>>> + return -EINVAL;
>>>> +
>>>> + qpg = virt_to_head_page(q->ring);
>>
>> Is it assured that q is initialized with a call to setsockopt
>> XDP_UMEM_FILL_RING before the call the mmap?
>
> Unfortunately not, so this is a bug. Case in point for running
> syzkaller below, definitely.
>
>> In general, with such an extensive new API, it might be worthwhile to
>> run syzkaller locally on a kernel with these patches. It is pretty
>> easy to set up
>> (https://github.com/google/syzkaller/blob/master/docs/linux/setup.md),
>> though it also needs to be taught about any new APIs.
>
> Good idea. Will set this up and have it torture the API.
>
> Thanks: Magnus
Great, thanks. I forgot to mention how to encode the new APIs for syzkaller:
https://github.com/google/syzkaller/blob/master/docs/syscall_descriptions.md
