linux-kernel - Re: [PATCH 2/2] xen/arm: introduce XENMEM_cache

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Date:	Thu, 2 Oct 2014 12:32:48 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<Ian.Campbell@...rix.com>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] xen/arm: introduce XENMEM_cache_flush

On Thu, 2 Oct 2014, David Vrabel wrote:
> On 02/10/14 11:06, Stefano Stabellini wrote:
> > Introduce support for new hypercall XENMEM_cache_flush.
> > Use it to perform cache flashing on pages used for dma when necessary.
> [...]
> > --- a/arch/arm/xen/mm32.c
> > +++ b/arch/arm/xen/mm32.c
> [...]
> > @@ -24,7 +27,21 @@ static void dma_cache_maint(dma_addr_t handle, unsigned long offset,
> >  	
> >  		if (!pfn_valid(pfn))
> >  		{
> > -			/* TODO: cache flush */
> > +			struct xen_cache_flush cflush;
> > +
> > +			cflush.op = 0;
> > +			cflush.addr = handle + offset;
> > +			cflush.size = size;
> > +
> > +			if (op == dmac_unmap_area && dir != DMA_TO_DEVICE)
> > +				cflush.op = XENMEM_CACHE_INVAL;
> > +			if (op == dmac_map_area) {
> > +				cflush.op = XENMEM_CACHE_CLEAN;
> > +				if (dir == DMA_FROM_DEVICE)
> > +					cflush.op |= XENMEM_CACHE_INVAL;
> > +			}
> > +			if (cflush.op)
> > +				HYPERVISOR_memory_op(XENMEM_cache_flush, &cflush);
> >  		} else {
> >  			struct page *page = pfn_to_page(pfn);
> >  
> [...]
> > --- a/include/xen/interface/memory.h
> > +++ b/include/xen/interface/memory.h
> > @@ -263,4 +263,20 @@ struct xen_remove_from_physmap {
> >  };
> >  DEFINE_GUEST_HANDLE_STRUCT(xen_remove_from_physmap);
> >  
> > +/*
> > + * Issue one or more cache maintenance operations on a memory range
> > + * owned by the calling domain or granted to the calling domain by a
> > + * foreign domain.
> > + */
> > +#define XENMEM_cache_flush                 27
> > +struct xen_cache_flush {
> > +/* addr is the machine address at the start of the memory range */
> 
> You say machine address here but call it with a bus address.  With no
> IOMMU these are equivalent but what's correct if an IOMMU is used?

I mean mfns, real machine addresses. With an IOMMU the hypercall should
not be used.

 
> > +uint64_t addr;
> > +uint64_t size;
> > +#define XENMEM_CACHE_CLEAN      (1<<0)
> > +#define XENMEM_CACHE_INVAL      (1<<1)
> > +uint32_t op;
> > +};
> > +DEFINE_GUEST_HANDLE_STRUCT(xen_cache_flush);
> > +
> >  #endif /* __XEN_PUBLIC_MEMORY_H__ */
> > 
> 
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