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SubjectRe: [PATCH 2/3] dm: add support for passing through inline crypto support
On Thu, Sep 24, 2020 at 09:40:22AM -0400, Mike Snitzer wrote:
> On Thu, Sep 24 2020 at 3:48am -0400,
> Satya Tangirala <satyat@google.com> wrote:
>
> > On Wed, Sep 23, 2020 at 09:21:03PM -0400, Mike Snitzer wrote:
> > > On Wed, Sep 09 2020 at 7:44pm -0400,
> > > Satya Tangirala <satyat@google.com> wrote:
> > >
> > > > From: Eric Biggers <ebiggers@google.com>
> > > >
> > > > Update the device-mapper core to support exposing the inline crypto
> > > > support of the underlying device(s) through the device-mapper device.
> > > >
> > > > This works by creating a "passthrough keyslot manager" for the dm
> > > > device, which declares support for encryption settings which all
> > > > underlying devices support. When a supported setting is used, the bio
> > > > cloning code handles cloning the crypto context to the bios for all the
> > > > underlying devices. When an unsupported setting is used, the blk-crypto
> > > > fallback is used as usual.
> > > >
> > > > Crypto support on each underlying device is ignored unless the
> > > > corresponding dm target opts into exposing it. This is needed because
> > > > for inline crypto to semantically operate on the original bio, the data
> > > > must not be transformed by the dm target. Thus, targets like dm-linear
> > > > can expose crypto support of the underlying device, but targets like
> > > > dm-crypt can't. (dm-crypt could use inline crypto itself, though.)
> > > >
> > > > When a key is evicted from the dm device, it is evicted from all
> > > > underlying devices.
> > > >
> > > > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > > > Co-developed-by: Satya Tangirala <satyat@google.com>
> > > > Signed-off-by: Satya Tangirala <satyat@google.com>
> > > > ---
> > > > block/blk-crypto.c | 1 +
> > > > block/keyslot-manager.c | 34 ++++++++++++
> > > > drivers/md/dm-core.h | 4 ++
> > > > drivers/md/dm-table.c | 52 +++++++++++++++++++
> > > > drivers/md/dm.c | 92 ++++++++++++++++++++++++++++++++-
> > > > include/linux/device-mapper.h | 6 +++
> > > > include/linux/keyslot-manager.h | 7 +++
> > > > 7 files changed, 195 insertions(+), 1 deletion(-)
> > > >
>
> > > > diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
> > > > index c4ef1fceead6..4542050eebfc 100644
> > > > --- a/drivers/md/dm-core.h
> > > > +++ b/drivers/md/dm-core.h
> > > > @@ -12,6 +12,7 @@
> > > > #include <linux/kthread.h>
> > > > #include <linux/ktime.h>
> > > > #include <linux/blk-mq.h>
> > > > +#include <linux/keyslot-manager.h>
> > > >
> > > > #include <trace/events/block.h>
> > > >
> > > > @@ -49,6 +50,9 @@ struct mapped_device {
> > > >
> > > > int numa_node_id;
> > > > struct request_queue *queue;
> > > > +#ifdef CONFIG_BLK_INLINE_ENCRYPTION
> > > > + struct blk_keyslot_manager ksm;
> > > > +#endif
> > > >
> > > > atomic_t holders;
> > > > atomic_t open_count;
> > >
> > > Any reason you placed the ksm member where you did?
> >
> > As in, any reason why it's placed right after the struct request_queue
> > *queue? The ksm is going to be set up in the request_queue and is a part
> > of the request_queue is some sense, so it seemed reasonable to me to
> > group them together....but I don't think there's any reason it *has* to
> > be there, if you think it should be put elsewhere (or maybe I'm
> > misunderstanding your question :) ).
>
> Placing the full struct where you did is highly disruptive to the prior
> care taken to tune alignment of struct members within mapped_device.
>
Ah I see - sorry about that! I ended up removing it entirely in the next
version of this series while trying to address this and your other
comments :). The next version is at

https://lore.kernel.org/linux-block/20201015214632.41951-5-satyat@google.com/

> Switching to a pointer will be less so, but even still it might be best
> to either find a hole in the struct (not looked recently, but there may
> not be one) or simply put it at the end of the structure.
>
> The pahole utility is very useful for this kind of struct member
> placement, etc. But it is increasingly unavailable in modern Linux
> distros...
>
> Mike
>

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