On Tue, 8 Dec 2020 at 14:25, David Howells <dhowells@xxxxxxxxxx> wrote: > > I wonder - would it make sense to reserve two arrays of scatterlist structs > and a mutex per CPU sufficient to map up to 1MiB of pages with each array > while the krb5 service is in use? > > That way sunrpc could, say, grab the mutex, map the input and output buffers, > do the entire crypto op in one go and then release the mutex - at least for > big ops, small ops needn't use this service. > > For rxrpc/afs's use case this would probably be overkill - it's doing crypto > on each packet, not on whole operations - but I could still make use of it > there. > > However, that then limits the maximum size of an op to 1MiB, plus dangly bits > on either side (which can be managed with chained scatterlist structs) and > also limits the number of large simultaneous krb5 crypto ops we can do. > Apparently, it is permitted for gss_krb5_cts_crypt() to do a kmalloc(GFP_NOFS) in the context from where gss_krb5_aes_encrypt() is being invoked, and so I don't see why it wouldn't be possible to simply kmalloc() a scatterlist[] of the appropriate size, populate it with all the pages, bufs and whatever else gets passed into the skcipher, and pass it into the skcipher in one go.
