[PATCH] firmware: arm_ffa: Add support for MEM_LEND

[Marc Bonnici]

Hi Jens,

> -----Original Message-----
> From: Jens Wiklander <jens.wiklander at linaro.org>
> Sent: 08 October 2021 08:49
> To: Marc Bonnici <Marc.Bonnici at arm.com>
> Cc: Linux ARM <linux-arm-kernel at lists.infradead.org>; Achin Gupta
> <Achin.Gupta at arm.com>; Arunachalam Ganapathy
> <Arunachalam.Ganapathy at arm.com>; Sudeep Holla <Sudeep.Holla at arm.com>;
> Coboy Chen <Coboy.Chen at mediatek.com>; Lukas Hanel
> <lukas.hanel at trustonic.com>; Lionel Pacoud
> <lionel.pacoud at trustonic.com>
> Subject: Re: [PATCH] firmware: arm_ffa: Add support for MEM_LEND
> 
> Hi Marc,
> 
> On Thu, Oct 7, 2021 at 7:44 PM Marc Bonnici <marc.bonnici at arm.com>
> wrote:
> >
> > As part of the FF-A spec, an endpoint is allowed to transfer
> access
> > of, or lend, a memory region to one or more borrowers.
> >
> > Extend the existing memory sharing implementation to support FF-A
> > MEM_LEND functionality and expose this to other kernel drivers.
> >
> > Signed-off-by: Marc Bonnici <marc.bonnici at arm.com>
> > ---
> >  drivers/firmware/arm_ffa/driver.c | 10 ++++++++++
> >  include/linux/arm_ffa.h           |  2 ++
> >  2 files changed, 12 insertions(+)
> 
> This is similar to MEM_SHARE, but with one significant difference,
> the memory lent may become inaccessible by the kernel once this has
> succeeded. In case there's no hypervisor in the system the
> responsibility falls on the kernel itself to make sure that it will
> keep off the lent memory. Even if it may not be the responsibility
> of this driver to enforce this it might be worth a comment to help
> the caller on the right track.
> 

Agreed, I don't think the responsibility itself should fall to this 
driver but a comment for a potential caller would certainly be useful,
shall update to include. 

Thanks,

Kind Regards
Marc Bonnici


> Cheers,
> Jens
> 
> >
> > diff --git a/drivers/firmware/arm_ffa/driver.c
> > b/drivers/firmware/arm_ffa/driver.c
> > index 6e0c883ab708..41661ae4ee04 100644
> > --- a/drivers/firmware/arm_ffa/driver.c
> > +++ b/drivers/firmware/arm_ffa/driver.c
> > @@ -613,6 +613,15 @@ ffa_memory_share(struct ffa_device *dev,
> struct ffa_mem_ops_args *args)
> >         return ffa_memory_ops(FFA_FN_NATIVE(MEM_SHARE), args);  }
> >
> > +static int
> > +ffa_memory_lend(struct ffa_device *dev, struct ffa_mem_ops_args
> > +*args) {
> > +       if (dev->mode_32bit)
> > +               return ffa_memory_ops(FFA_MEM_LEND, args);
> > +
> > +       return ffa_memory_ops(FFA_FN_NATIVE(MEM_LEND), args); }
> > +
> >  static const struct ffa_dev_ops ffa_ops = {
> >         .api_version_get = ffa_api_version_get,
> >         .partition_info_get = ffa_partition_info_get, @@ -620,6
> +629,7
> > @@ static const struct ffa_dev_ops ffa_ops = {
> >         .sync_send_receive = ffa_sync_send_receive,
> >         .memory_reclaim = ffa_memory_reclaim,
> >         .memory_share = ffa_memory_share,
> > +       .memory_lend = ffa_memory_lend,
> >  };
> >
> >  const struct ffa_dev_ops *ffa_dev_ops_get(struct ffa_device *dev)
> > diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
> index
> > 505c679b6a9b..85651e41ded8 100644
> > --- a/include/linux/arm_ffa.h
> > +++ b/include/linux/arm_ffa.h
> > @@ -262,6 +262,8 @@ struct ffa_dev_ops {
> >         int (*memory_reclaim)(u64 g_handle, u32 flags);
> >         int (*memory_share)(struct ffa_device *dev,
> >                             struct ffa_mem_ops_args *args);
> > +       int (*memory_lend)(struct ffa_device *dev,
> > +                          struct ffa_mem_ops_args *args);
> >  };
> >
> >  #endif /* _LINUX_ARM_FFA_H */
> > --
> > 2.25.1
> >