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SubjectRe: [PATCH v9 10/13] xen/arm/arm64: introduce xen_arch_need_swiotlb
On Wed, 12 Nov 2014, Stefano Stabellini wrote:
> Introduce an arch specific function to find out whether a particular dma
> mapping operation needs to bounce on the swiotlb buffer.
>
> On ARM and ARM64, if the page involved is a foreign page and the device
> is not coherent, we need to bounce because at unmap time we cannot
> execute any required cache maintenance operations (we don't know how to
> find the pfn from the mfn).
>
> No change of behaviour for x86.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> Reviewed-by: David Vrabel <david.vrabel@citrix.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

I am thinking of asking a backport of this patch to 3.16+

The catch is that is_device_dma_coherent is not available on older
kernels, so I'll have to change the arm implementation of
xen_arch_need_swiotlb to:

+bool xen_arch_need_swiotlb(struct device *dev,
+ unsigned long pfn,
+ unsigned long mfn)
+{
+ return pfn != mfn;
+}
+

It is going to make things slower but it is going to fix the issue with
cache flushing buffers for non-coherent devices.

Konrad, are you OK with that?


> Changes in v6:
> - fix ts.
>
> Changes in v5:
> - fix indentation.
> ---
> arch/arm/include/asm/xen/page.h | 4 ++++
> arch/arm/xen/mm.c | 7 +++++++
> arch/x86/include/asm/xen/page.h | 7 +++++++
> drivers/xen/swiotlb-xen.c | 5 ++++-
> 4 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index 135c24a..68c739b 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -107,4 +107,8 @@ static inline bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
> #define xen_remap(cookie, size) ioremap_cache((cookie), (size))
> #define xen_unmap(cookie) iounmap((cookie))
>
> +bool xen_arch_need_swiotlb(struct device *dev,
> + unsigned long pfn,
> + unsigned long mfn);
> +
> #endif /* _ASM_ARM_XEN_PAGE_H */
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index ab700e1..28ebf3e 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -100,6 +100,13 @@ void __xen_dma_sync_single_for_device(struct device *hwdev,
> __xen_dma_page_cpu_to_dev(hwdev, handle, size, dir);
> }
>
> +bool xen_arch_need_swiotlb(struct device *dev,
> + unsigned long pfn,
> + unsigned long mfn)
> +{
> + return ((pfn != mfn) && !is_device_dma_coherent(dev));
> +}
> +
> int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> unsigned int address_bits,
> dma_addr_t *dma_handle)
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index c949923..f58ef6c 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -236,4 +236,11 @@ void make_lowmem_page_readwrite(void *vaddr);
> #define xen_remap(cookie, size) ioremap((cookie), (size));
> #define xen_unmap(cookie) iounmap((cookie))
>
> +static inline bool xen_arch_need_swiotlb(struct device *dev,
> + unsigned long pfn,
> + unsigned long mfn)
> +{
> + return false;
> +}
> +
> #endif /* _ASM_X86_XEN_PAGE_H */
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index ad2c5eb..3725ee4 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -399,7 +399,9 @@ dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page,
> * buffering it.
> */
> if (dma_capable(dev, dev_addr, size) &&
> - !range_straddles_page_boundary(phys, size) && !swiotlb_force) {
> + !range_straddles_page_boundary(phys, size) &&
> + !xen_arch_need_swiotlb(dev, PFN_DOWN(phys), PFN_DOWN(dev_addr)) &&
> + !swiotlb_force) {
> /* we are not interested in the dma_addr returned by
> * xen_dma_map_page, only in the potential cache flushes executed
> * by the function. */
> @@ -557,6 +559,7 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl,
> dma_addr_t dev_addr = xen_phys_to_bus(paddr);
>
> if (swiotlb_force ||
> + xen_arch_need_swiotlb(hwdev, PFN_DOWN(paddr), PFN_DOWN(dev_addr)) ||
> !dma_capable(hwdev, dev_addr, sg->length) ||
> range_straddles_page_boundary(paddr, sg->length)) {
> phys_addr_t map = swiotlb_tbl_map_single(hwdev,
> --
> 1.7.10.4
>


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