Re: [PATCH] RDMA/rxe: For invalidate compare keys according to the MR access

From: haris iqbal <haris.phnx@gmail.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Pearson, Robert B" <robert.pearson2@hpe.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"zyjzyj2000@gmail.com" <zyjzyj2000@gmail.com>,
	"aleksei.marov@ionos.com" <aleksei.marov@ionos.com>,
	"leon@kernel.org" <leon@kernel.org>,
	"haris.iqbal@ionos.com" <haris.iqbal@ionos.com>,
	"jinpu.wang@ionos.com" <jinpu.wang@ionos.com>,
	"rpearsonhpe@gmail.com" <rpearsonhpe@gmail.com>
Subject: Re: [PATCH] RDMA/rxe: For invalidate compare keys according to the MR access
Date: Thu, 7 Jul 2022 09:32:14 +0200	[thread overview]
Message-ID: <CAE_WKMz0u43YjoFs=QTpLAOdb_LEEf5es6UL4eWbU9U+OYQUNA@mail.gmail.com> (raw)
In-Reply-To: <20220706163948.GL23621@ziepe.ca>

On Wed, Jul 6, 2022 at 6:39 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Wed, Jul 06, 2022 at 05:41:08AM +0200, haris iqbal wrote:
> > On Tue, Jul 5, 2022 at 4:00 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > >
> > > On Tue, Jul 05, 2022 at 11:28:59AM +0200, haris iqbal wrote:
> > > > On Wed, Jun 29, 2022 at 8:48 PM Pearson, Robert B
> > > > <robert.pearson2@hpe.com> wrote:
> > > > >
> > > > > > > > If the rkey's and lkeys are always the same why do we store them twice in the mr ?
> > > > > > >
> > > > > > > They are not always the same currently. If you request remote access they are the same if you don't rkey is set to zero.
> > > > > > > You could, of course, check both the keys and the access bits but that is not the way it is written currently.
> > > > >
> > > > > > Storing the rkey instead of checking the flags seems like a weird obfuscation to me..
> > > > >
> > > > > > Jason
> > > > >
> > > > > One always has the choice to always just use the lkey and check the flags. But referring the rkey just uses one memory reference 😊
> > > >
> > > > Have we reached a consensus here as to how to solve this?
> > > >
> > > > This (and the issue created by dual map) has basically caused a
> > > > regression in RTRS since the 5.15. And we would appreciate it a lot if
> > > > the fix goes in and is backported.
> > >
> > > I think your patch is close, it should just be tweaked a bit.
> >
> > I couldn't conclude from the conversation above what that tweak should
> > be, if a conclusion has been reached. If not, then I'll wait.
>
> The 'rkey' input can be an lkey or rkey, and in rxe the lkey or rkey
> have the same value, including the variant bits.
>
> So, don't check based on the flags, if the rkey is not 0 check it,
> otherwise check the lkey
>
> Since we already did a lookup on the non-varient bits to get this far,
> the check's only purpose is to confirm that the wqe has the correct
> variant bits.

Thanks Jason. I sent the patch with the changes suggested. Also, I
stole your comment and used it as commit message, since that described
the changes accurately. :)

>
> Jason