Re: [rdma-rc 13/14] RDMA/mthca: Make explicit conversion to 64bit value

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Mon, Jul 31, 2017 at 04:23:52PM +0000, Bart Van Assche wrote:
> On Mon, 2017-07-31 at 19:16 +0300, Leon Romanovsky wrote:
> > On Mon, Jul 31, 2017 at 03:17:24PM +0000, Bart Van Assche wrote:
> > > On Mon, 2017-07-31 at 10:09 +0300, Leon Romanovsky wrote:
> > > > From: Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> > > >
> > > > The "lg" variable is declared as int so in all places where
> > > > this variable is used as a shift operand, the output will be
> > > > int too.
> > > >
> > > > This produces the following smatch warning:
> > > > drivers/infiniband/hw/mthca/mthca_cmd.c:701 mthca_map_cmd() warn:
> > > > 	should '1 << lg' be a 64 bit type?
> > > >
> > > > Simple declaration of "1" to be "1ULL" will fix the issue.
> > > >
> > > > Signed-off-by: Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> > > > Signed-off-by: Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> > > > ---
> > > >  drivers/infiniband/hw/mthca/mthca_cmd.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/infiniband/hw/mthca/mthca_cmd.c b/drivers/infiniband/hw/mthca/mthca_cmd.c
> > > > index 9d83a53c0c67..1052c35f2e75 100644
> > > > --- a/drivers/infiniband/hw/mthca/mthca_cmd.c
> > > > +++ b/drivers/infiniband/hw/mthca/mthca_cmd.c
> > > > @@ -698,7 +698,7 @@ static int mthca_map_cmd(struct mthca_dev *dev, u16 op, struct mthca_icm *icm,
> > > >  		for (i = 0; i < mthca_icm_size(&iter) >> lg; ++i) {
> > > >  			if (virt != -1) {
> > > >  				pages[nent * 2] = cpu_to_be64(virt);
> > > > -				virt += 1 << lg;
> > > > +				virt += 1ULL << lg;
> > > >  			}
> > > >
> > > >  			pages[nent * 2 + 1] =
> > >
> > > Hello Leon,
> > >
> > > Is my analysis correct that lg can be equal to or larger than 32? If so,
> > > isn't this patch a bug fix that needs a "Fixes:" tag?
> >
> > This is the fix to commit introduced in pre-git era and I don't have
> > adequate Fixes tag. The fact that no one complained about the problem
> > suggests to me that no one is really important to have it in stable trees.
> >
> > Tariq and me did the analysis for the same code issue with mlx4 (he is
> > planning to forward the fix to Dave) and our conclusion that it is not
> > bug.
> >
> > The reason to it in line 689:drivers/infiniband/hw/mthca/mthca_cmd.c
> >  689                 lg = ffs(mthca_icm_addr(&iter) | mthca_icm_size(&iter)) - 1;
> >
> > The "lg" for sure will be less than 31, because ffs returns values from 0 to 31 and minus 1.
> > The situation that ffs will return 0 is unlikely to happen.
>
> Hello Leon,
>
> mthca_icm_addr() returns a DMA address (dma_addr_t). Does that mean that
> that function can return a 64-bit value on 64-bit systems? Shouldn't ffs()
> be changed into a function that supports 64-bit values?

Don't dismiss the second part of that ffs: "| mthca_icm_size(&iter)", to
overflow ffs, the icm size should be more than 2^32. Is it real scenario?

>
> Thanks,
>
> Bart.
>

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