Re: [Xen-devel] [PATCH] swiotlb: fix phys_addr_t overflow warning

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Jun 17, 2019 at 09:13:16AM -0700, Stefano Stabellini wrote:
> On Mon, 17 Jun 2019, Arnd Bergmann wrote:
> > On architectures that have a larger dma_addr_t than phys_addr_t,
> > the swiotlb_tbl_map_single() function truncates its return code
> > in the failure path, making it impossible to identify the error
> > later, as we compare to the original value:
> > 
> > kernel/dma/swiotlb.c:551:9: error: implicit conversion from 'dma_addr_t' 
> > (aka 'unsigned long long') to 'phys_addr_t' (aka 'unsigned int') changes 
> > value from 18446744073709551615 to 4294967295 
> > [-Werror,-Wconstant-conversion]
> >         return DMA_MAPPING_ERROR;
> > 
> > Use an explicit typecast here to convert it to the narrower type,
> > and use the same expression in the error handling later.
> > 
> > Fixes: b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> 
> Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

queued.
> 
> 
> > ---
> > I still think that reverting the original commit would have
> > provided clearer semantics for this corner case, but at least
> > this patch restores the correct behavior.
> > ---
> >  drivers/xen/swiotlb-xen.c | 2 +-
> >  kernel/dma/swiotlb.c      | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> > index d53f3493a6b9..cfbe46785a3b 100644
> > --- a/drivers/xen/swiotlb-xen.c
> > +++ b/drivers/xen/swiotlb-xen.c
> > @@ -402,7 +402,7 @@ static dma_addr_t xen_swiotlb_map_page(struct device 
> > *dev, struct page *page,
> >  
> >     map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir,
> >                                  attrs);
> > -   if (map == DMA_MAPPING_ERROR)
> > +   if (map == (phys_addr_t)DMA_MAPPING_ERROR)
> >             return DMA_MAPPING_ERROR;
> >  
> >     dev_addr = xen_phys_to_bus(map);
> > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> > index e906ef2e6315..a3be651973ad 100644
> > --- a/kernel/dma/swiotlb.c
> > +++ b/kernel/dma/swiotlb.c
> > @@ -548,7 +548,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
> >     if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit())
> >             dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes), total 
> > %lu (slots), used %lu (slots)\n",
> >                      size, io_tlb_nslabs, tmp_io_tlb_used);
> > -   return DMA_MAPPING_ERROR;
> > +   return (phys_addr_t)DMA_MAPPING_ERROR;
> >  found:
> >     io_tlb_used += nslots;
> >     spin_unlock_irqrestore(&io_tlb_lock, flags);
> > @@ -666,7 +666,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys, 
> > dma_addr_t *dma_addr,
> >     /* Oh well, have to allocate and map a bounce buffer. */
> >     *phys = swiotlb_tbl_map_single(dev, __phys_to_dma(dev, io_tlb_start),
> >                     *phys, size, dir, attrs);
> > -   if (*phys == DMA_MAPPING_ERROR)
> > +   if (*phys == (phys_addr_t)DMA_MAPPING_ERROR)
> >             return false;
> >  
> >     /* Ensure that the address returned is DMA'ble */
> > -- 
> > 2.20.0
> > 

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