>
> On Mon, Feb 01, 2021 at 10:30:17AM -0800, Jianxiong Gao wrote:
> > @@ -868,12 +871,24 @@ static blk_status_t nvme_map_data(struct nvme_dev
> *dev, struct request *req,
> >       if (!iod->nents)
> >               goto out_free_sg;
> >
> > +     offset_ret = dma_set_min_align_mask(dev->dev, NVME_CTRL_PAGE_SIZE
> - 1);
> > +     if (offset_ret) {
> > +             dev_warn(dev->dev, "dma_set_min_align_mask failed to set
> offset\n");
> > +             goto out_free_sg;
> > +     }
> > +
> >       if (is_pci_p2pdma_page(sg_page(iod->sg)))
> >               nr_mapped = pci_p2pdma_map_sg_attrs(dev->dev, iod->sg,
> >                               iod->nents, rq_dma_dir(req),
> DMA_ATTR_NO_WARN);
> >       else
> >               nr_mapped = dma_map_sg_attrs(dev->dev, iod->sg, iod->nents,
> >                                            rq_dma_dir(req),
> DMA_ATTR_NO_WARN);
> > +
> > +     offset_ret = dma_set_min_align_mask(dev->dev, 0);
> > +     if (offset_ret) {
> > +             dev_warn(dev->dev, "dma_set_min_align_mask failed to reset
> offset\n");
> > +             goto out_free_sg;
> > +     }
> >       if (!nr_mapped)
> >               goto out_free_sg;
>
> Why is this setting being done and undone on each IO? Wouldn't it be
> more efficient to set it once during device initialization?
>
> And more importantly, this isn't thread safe: one CPU may be setting the
> device's dma alignment mask to 0 while another CPU is expecting it to be
> NVME_CTRL_PAGE_SIZE - 1.
>

I was having trouble getting the OS booted when setting it once during
initialization. However when I rebased to the latest rc6 this morning it
seems to be working with setting the mask on probe. I am still testing out
and will appreciate any idea what may cause the nvme driver to fail
with a single mask.

-- 
Jianxiong Gao