Re: [PATCH 1/7] ublk: widen ublk_shmem_buf_reg.len to __u64 for 4GB buffer support

[Ming Lei <tom.leiming@gmail.com>]

On Tue, Apr 14, 2026 at 11:40:36AM -0700, Caleb Sander Mateos wrote:
> On Thu, Apr 9, 2026 at 6:30 AM Ming Lei <tom.leiming@gmail.com> wrote:
> >
> > The __u32 len field cannot represent a 4GB buffer (0x100000000
> > overflows to 0). Change it to __u64 so buffers up to 4GB can be
> > registered. Add a reserved field for alignment and validate it
> > is zero.
> >
> > The kernel enforces a default max of 4GB (UBLK_SHMEM_BUF_SIZE_MAX)
> > which may be increased in future.
> >
> > Signed-off-by: Ming Lei <tom.leiming@gmail.com>
> > ---
> >  drivers/block/ublk_drv.c      | 9 ++++++++-
> >  include/uapi/linux/ublk_cmd.h | 3 ++-
> >  2 files changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> > index 2e475bdc54dd..ada9a2e32ea9 100644
> > --- a/drivers/block/ublk_drv.c
> > +++ b/drivers/block/ublk_drv.c
> > @@ -63,6 +63,9 @@
> >  #define UBLK_CMD_REG_BUF       _IOC_NR(UBLK_U_CMD_REG_BUF)
> >  #define UBLK_CMD_UNREG_BUF     _IOC_NR(UBLK_U_CMD_UNREG_BUF)
> >
> > +/* Default max shmem buffer size: 4GB (may be increased in future) */
> > +#define UBLK_SHMEM_BUF_SIZE_MAX        (1ULL << 32)
> > +
> >  #define UBLK_IO_REGISTER_IO_BUF                _IOC_NR(UBLK_U_IO_REGISTER_IO_BUF)
> >  #define UBLK_IO_UNREGISTER_IO_BUF      _IOC_NR(UBLK_U_IO_UNREGISTER_IO_BUF)
> >
> > @@ -5351,11 +5354,15 @@ static int ublk_ctrl_reg_buf(struct ublk_device *ub,
> >         if (buf_reg.flags & ~UBLK_SHMEM_BUF_READ_ONLY)
> >                 return -EINVAL;
> >
> > +       if (buf_reg.reserved)
> > +               return -EINVAL;
> > +
> >         addr = buf_reg.addr;
> >         size = buf_reg.len;
> >         nr_pages = size >> PAGE_SHIFT;
> >
> > -       if (!size || !PAGE_ALIGNED(size) || !PAGE_ALIGNED(addr))
> > +       if (!size || size > UBLK_SHMEM_BUF_SIZE_MAX ||
> 
> Should be >=? Otherwise, LGTM.

It should be ">" because we do want to support 4GB size buffer.


Thanks,
Ming