Re: [PATCH v9 10/13] xen/arm/arm64: introduce xen_arch_need_swiotlb

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Nov 21, 2014 at 04:31:31PM +0000, Stefano Stabellini wrote:
> 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?

Looks fine.
> 
> 
> > 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
> >