Re: [PATCH v2] sparc: Fix page alignment in dma mapping

On Wed, Feb 18, 2026 at 12:09:06PM +0100, Stian Halseth wrote:
> On Wed, 2026-02-18 at 11:28 +0100, Marek Szyprowski wrote:
> > On 17.02.2026 18:10, [email protected] wrote:
> > > From: Stian Halseth <[email protected]>
> > > 
> > > 'phys' may include an offset within the page, while 'base_paddr' is
> > > already
> > > page-aligned. This caused incorrect DMA mapping in dma_4u_map_phys
> > > and
> > > dma_4v_map_phys.
> > > 
> > > Fix both functions by masking phys with IO_PAGE_MASK or subtracting
> > > the
> > > page offset, covering both generic SPARC code and sun4v.
> > > 
> > > Fixes: 38c0d0ebf520 ("sparc: Use physical address DMA mapping")
> > > Reported-by: Stian Halseth <[email protected]>
> > > Closes: https://protect2.fireeye.com/v1/url?k=4d8fbc00-1214850c-
> > > 4d8e374f-000babff3563-ee1be24be576e072&q=1&e=0f8967ce-f558-4339-
> > > bddb-
> > > f324ec46c035&u=https%3A%2F%2Fgithub.com%2Fsparclinux%2Fissues%2Fiss
> > > ues%2F75
> > > Suggested-by: Marek Szyprowski <[email protected]>
> > > Signed-off-by: Stian Halseth <[email protected]>
> > > ---
> > >   arch/sparc/kernel/iommu.c     | 2 ++
> > >   arch/sparc/kernel/pci_sun4v.c | 2 +-
> > >   2 files changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/sparc/kernel/iommu.c b/arch/sparc/kernel/iommu.c
> > > index 46ef88bc9c26..f3755a388ac7 100644
> > > --- a/arch/sparc/kernel/iommu.c
> > > +++ b/arch/sparc/kernel/iommu.c
> > > @@ -312,6 +312,8 @@ static dma_addr_t dma_4u_map_phys(struct device
> > > *dev, phys_addr_t phys,
> > >    if (direction != DMA_TO_DEVICE)
> > >    iopte_protection |= IOPTE_WRITE;
> > >   
> > > + phys -= offset_in_page(phys);
> > > +
> > 
> > I've just noticed that IO_PAGE_SIZE might not equal to PAGE_SIZE (not
> > sure if this is true in case of SPARCs), so it would be better to
> > rely 
> > on IO_PAGE_MASK or IO_PAGE_SIZE only. Just unify the fix for the both
> > affected functions either by masking phys with IO_PAGE_SIZE where it
> > is 
> > used or by subtracting (phys & ~IO_PAGE_MASK) from it.
> > 
> 
> Good point, and thanks for the review.
> 
> I failed to consider that the offset_in_page is based on PAGE_SIZE, not
> IO_PAGE_SIZE.
> 
> Suggestion, subtract IO_PAGE_MASK in both functions.
> 
> arch/sparc/kernel/iommu.c:
>  -phys -= offset_in_page(phys)
>  +phys &= IO_PAGE_MASK;
> 
> 
> arch/sparc/kernel/pci_sun4v.c (better to subtract before loop?):
>  +phys &= IO_PAGE_MASK;
> 
>  for (i = 0; i < npages; i++, phys += IO_PAGE_SIZE) {
>          -long err = iommu_batch_add(phys & IO_PAGE_MASK, mask);
>          +long err = iommu_batch_add(phys, mask);
>          if (unlikely(err < 0L))
>                  goto iommu_map_fail;
>  }
> 
> Is this acceptable, and in line with kernel coding style?
> 
> If yes, I can submit patch v3 with this proposed change.
> 
> And Patch v3, should be sent using the message ID of this review
> response, right? Still learning :)

No, just send patch v3 without Reply-To field. Add changelog under ---
trailer line and describe changes.

Thanks