On Tue, Apr 30, 2019 at 07:18:10AM -0700, Matthew Wilcox wrote: > On Tue, Apr 30, 2019 at 02:24:05PM +0100, Mark Rutland wrote: > > In io_sqe_buffer_register() we allocate a number of arrays based on the > > iov_len from the user-provided iov. While we limit iov_len to SZ_1G, > > we can still attempt to allocate arrays exceeding MAX_ORDER. > > > > On a 64-bit system with 4KiB pages, for an iov where iov_base = 0x10 and > > iov_len = SZ_1G, we'll calculate that nr_pages = 262145. When we try to > > allocate a corresponding array of (16-byte) bio_vecs, requiring 4194320 > > bytes, which is greater than 4MiB. This results in SLUB warning that > > we're trying to allocate greater than MAX_ORDER, and failing the > > allocation. > > > > Avoid this by passing __GFP_NOWARN when allocating arrays for the > > user-provided iov_len. We'll gracefully handle the failed allocation, > > returning -ENOMEM to userspace. > > > > We should probably consider lowering the limit below SZ_1G, or reworking > > the array allocations. > > I'd suggest that kvmalloc is probably our friend here ... we don't really > want to return -ENOMEM to userspace for this case, I don't think. Sure. I'll go verify that the uring code doesn't assume this memory is physically contiguous. I also guess we should be passing GFP_KERNEL_ACCOUNT rateh than a plain GFP_KERNEL. Thanks, Mark.
