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SubjectRe: [PATCH] swiotlb: fix phys_addr_t overflow warning
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@arndb.de>
>
> Acked-by: Stefano Stabellini <sstabellini@kernel.org>

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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