Hi Herbert, > -----Original Message----- > From: Herbert Xu [mailto:herbert@xxxxxxxxxxxxxxxxxxx] > Sent: Friday, September 18, 2015 4:50 PM > To: Porosanu Alexandru-B06830 <alexandru.porosanu@xxxxxxxxxxxxx> > Cc: linux-crypto@xxxxxxxxxxxxxxx; Geanta Neag Horia Ioan-B05471 > <Horia.Geanta@xxxxxxxxxxxxx>; Pop Mircea-R19439 > <mircea.pop@xxxxxxxxxxxxx> > Subject: Re: [PATCH v2] crypto/caam: add backlogging support > > On Fri, Sep 18, 2015 at 01:46:50PM +0000, Porosanu Alexandru wrote: > > > > Before this patch, for CAAM driver, regardless if a tfm has > > MAY_BACKLOG set or not, if there are no more slots available in the HW JR, > the API will return -EBUSY, but the request will _not_ be saved for future > processing. That's wrong, and as a result, dm-crypt _hangs_ when using > CAAM offloaded algorithms. > > I understand that the current driver is buggy. However your fix is broken > too. MAY_BACKLOG must be reliable and that means not dropping requests. MAY_BACKLOG requests will fail once you run out of memory (f.i. backlogging using crypto_queue) Now, for this patch requests will be dropped if there are no more "backlogging" slots available. Would limiting the # of tfms w/MAY_BACKLOG associated with the driver to the # of backlogging slots be OK? > > > Now, the proposed patch sets aside a # of HW slots that will be used for > storing "backloggable" requests. The purpose of this is to ensure that never > will the JR drop a "backloggable" request, but they will be stored for eventual > processing (when the HW read pointer reaches the respective slot). > > More to the point this patch does the following: 1 enqueue is accepted (if > MAY_BACKLOG is set on the tfm), but the API will return -EBUSY, iff there > are less than <threshold> slots available in the HW JR. > > For non-backloggable requests (or when the HW JR is sufficiently empty) > are treated w/o any change. One observation would be that this change is > completely transparent to the HW, which works in the same way as before. > > What I was trying to point out in the caveat above is that a rogue user > which will keep on enqueing requests, will eventually be denied and the > requests _will_ be dropped. > > As a side-observation, for crypto_queues, the limit is the available > memory, so a bad-behaved user will generate an OOM. > > Yes there is a resource control issue but that should be handled by limiting > the number of tfms and not an arbitrary limit in the driver. Let me try and put it another way: for each tfm w/MAY_BACKLOG, the driver will accept a request and will return -EBUSY. Once there are really no more slots available, yes, requests will get dropped (i.e. -EIO will be returned) > > Cheers, > -- > Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: > http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt Thanks, Alex P. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
