On Fri, 14 Feb 2025 11:55:47 -0500 Steven Rostedt <[email protected]> wrote:
> From: Steven Rostedt <[email protected]> .... > The reason was that the code that maps the ring buffer pages to user space > has: > > page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); ... > But virt_to_page() does not work with vmap()'d memory which is what the > persistent ring buffer has. It is rather trivial to allow this, but for > now just disable mmap() of instances that have their ring buffer from the > reserve_mem option. I've recently fallen foul of the same issue elsewhere [1]. Perhaps there ought to be a variant of virt_to_page() that returns an error for addresses outside the kernel map. Or even a fast version that doesn't check for places where the cost of the additional conditional would matter. Even a kernel panic for an unchecked NULL pointer would be easier to diagnose than the current situation. [1] In my case it was dma_alloc_coherent() using vmalloc() when an iommu is enabled and then the wrong things happening when I try to mmap() the buffer into userspace (offset in both the dma buffer and the user file). I do need to check that the iommu is honouring the buffer alignment. David
