Re: [PATCH v2][next] dmaengine: dw-edma: Check MSI descriptor before copying

[Alan Mikhak]

On Thu, Apr 23, 2020 at 2:28 AM Gustavo Pimentel
<Gustavo.Pimentel@xxxxxxxxxxxx> wrote:
>
> On Thu, Apr 23, 2020 at 2:58:21, Alan Mikhak <alan.mikhak@xxxxxxxxxx>
> wrote:
>
> > From: Alan Mikhak <alan.mikhak@xxxxxxxxxx>
> >
> > Modify dw_edma_irq_request() to check if a struct msi_desc entry exists
> > before copying the contents of its struct msi_msg pointer.
> >
> > Without this sanity check, __get_cached_msi_msg() crashes when invoked by
> > dw_edma_irq_request() running on a Linux-based PCIe endpoint device. MSI
> > interrupt are not received by PCIe endpoint devices. If irq_get_msi_desc()
> > returns null, then there is no cached struct msi_msg to be copied.
> >
> > This patch depends on the following patch:
> > [PATCH v2] dmaengine: dw-edma: Decouple dw-edma-core.c from struct pci_dev
> > https://urldefense.com/v3/__https://patchwork.kernel.org/patch/11491757/__;!!A4F2R9G_pg!L_vf_Tml7Ca4sWVvZp5crRCp7YsMj6B93G9cMAO8Dj3w9I0MArjwuwNKtDz9rr0RlpXiqPg$
> >
> > Rebased on linux-next which has above patch applied.
> >
> > Fixes: Build error with config x86_64-randconfig-f003-20200422
> > Fixes: Build error with config s390-allmodconfig
> > Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Alan Mikhak <alan.mikhak@xxxxxxxxxx>
> > ---
> >  drivers/dma/dw-edma/dw-edma-core.c | 17 ++++++++++-------
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> > index db401eb11322..306ab50462be 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/dmaengine.h>
> >  #include <linux/err.h>
> >  #include <linux/interrupt.h>
> > +#include <linux/irq.h>
> >  #include <linux/dma/edma.h>
> >  #include <linux/dma-mapping.h>
> >
> > @@ -773,6 +774,7 @@ static int dw_edma_irq_request(struct dw_edma_chip *chip,
> >       u32 rd_mask = 1;
> >       int i, err = 0;
> >       u32 ch_cnt;
> > +     int irq;
> >
> >       ch_cnt = dw->wr_ch_cnt + dw->rd_ch_cnt;
> >
> > @@ -781,16 +783,16 @@ static int dw_edma_irq_request(struct dw_edma_chip *chip,
> >
> >       if (dw->nr_irqs == 1) {
> >               /* Common IRQ shared among all channels */
> > -             err = request_irq(dw->ops->irq_vector(dev, 0),
> > -                               dw_edma_interrupt_common,
> > +             irq = dw->ops->irq_vector(dev, 0);
> > +             err = request_irq(irq, dw_edma_interrupt_common,
> >                                 IRQF_SHARED, dw->name, &dw->irq[0]);
> >               if (err) {
> >                       dw->nr_irqs = 0;
> >                       return err;
> >               }
> >
> > -             get_cached_msi_msg(dw->ops->irq_vector(dev, 0),
> > -                                &dw->irq[0].msi);
> > +             if (irq_get_msi_desc(irq))
> > +                     get_cached_msi_msg(irq, &dw->irq[0].msi);
> >       } else {
> >               /* Distribute IRQs equally among all channels */
> >               int tmp = dw->nr_irqs;
> > @@ -804,7 +806,8 @@ static int dw_edma_irq_request(struct dw_edma_chip *chip,
> >               dw_edma_add_irq_mask(&rd_mask, *rd_alloc, dw->rd_ch_cnt);
> >
> >               for (i = 0; i < (*wr_alloc + *rd_alloc); i++) {
> > -                     err = request_irq(dw->ops->irq_vector(dev, i),
> > +                     irq = dw->ops->irq_vector(dev, i);
> > +                     err = request_irq(irq,
> >                                         i < *wr_alloc ?
> >                                               dw_edma_interrupt_write :
> >                                               dw_edma_interrupt_read,
> > @@ -815,8 +818,8 @@ static int dw_edma_irq_request(struct dw_edma_chip *chip,
> >                               return err;
> >                       }
> >
> > -                     get_cached_msi_msg(dw->ops->irq_vector(dev, i),
> > -                                        &dw->irq[i].msi);
> > +                     if (irq_get_msi_desc(irq))
> > +                             get_cached_msi_msg(irq, &dw->irq[i].msi);
> >               }
> >
> >               dw->nr_irqs = i;
> > --
> > 2.7.4
>
>
> Acked-by: Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>

Thanks Gustavo for the Ack.

FYI, I first considered adding an ops function to decouple dw-edma-core.c
from struct msi_msg. However, in a separate use case that I have in mind,
dw-edma would run on a host system having Synopsys DesignWare PCI eDMA
hardware on the host-side. In this use case, the host system eDMA engines
may be used in conjunction with an endpoint device also having the same
eDMA hardware. In this use case, dw-edma running on the host would need
to call get_cached_msi_msg() just in case the host has an msi_msg cached
from the endpoint device. As a result, I opted to not add a new ops
function.

Regards,
Alan

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