On 4/30/19 8:59 AM, Mark Rutland wrote: > 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. kvmalloc() is fine, the io_uring code doesn't care about the layout of the memory, it just uses it as an index. -- Jens Axboe
