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

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Message-ID: <542D2BC2.2040505@citrix.com>
Date:	Thu, 2 Oct 2014 11:41:06 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<xen-devel@...ts.xensource.com>
CC:	<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 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?

David

> +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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