Re: [Xen-devel] [PATCH v2 2/2] xen/arm: introduce GNTTABOP_cache_flush

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 03/10/14 15:53, Stefano Stabellini wrote:
> Introduce support for new hypercall GNTTABOP_cache_flush.
> Use it to perform cache flashing on pages used for dma when necessary.
[..]
>  /* functions called by SWIOTLB */
> @@ -22,16 +25,31 @@ static void dma_cache_maint(dma_addr_t handle, unsigned 
> long offset,
>               size_t len = left;
>               void *vaddr;
>       
> +             if (len + offset > PAGE_SIZE)
> +                     len = PAGE_SIZE - offset;
> +
>               if (!pfn_valid(pfn))
>               {
> -                     /* TODO: cache flush */
> +                     struct gnttab_cache_flush cflush;
> +
> +                     cflush.op = 0;
> +                     cflush.a.dev_bus_addr = pfn << PAGE_SHIFT;
> +                     cflush.offset = offset;
> +                     cflush.size = len;
> +
> +                     if (op == dmac_unmap_area && dir != DMA_TO_DEVICE)
> +                             cflush.op = GNTTAB_CACHE_INVAL;
> +                     if (op == dmac_map_area) {
> +                             cflush.op = GNTTAB_CACHE_CLEAN;
> +                             if (dir == DMA_FROM_DEVICE)
> +                                     cflush.op |= GNTTAB_CACHE_INVAL;
> +                     }

Are all these cache operations needed?  You do a clean on map regardless
of the direction and INVAL on map seems unnecessary.

I would have thought it would be:

map && (TO_DEVICE || BOTH)
   op = CLEAN

unmap && (FROM_DEVICE || BOTH)
   op = INVAL

> --- a/include/xen/interface/grant_table.h
> +++ b/include/xen/interface/grant_table.h
> @@ -479,6 +479,24 @@ struct gnttab_get_version {
>  DEFINE_GUEST_HANDLE_STRUCT(gnttab_get_version);
>  
>  /*
> + * Issue one or more cache maintenance operations on a portion of a
> + * page granted to the calling domain by a foreign domain.
> + */
> +#define GNTTABOP_cache_flush          12
> +struct gnttab_cache_flush {
> +    union {
> +        uint64_t dev_bus_addr;
> +        grant_ref_t ref;
> +    } a;
> +    uint32_t offset; /* offset from start of grant */
> +    uint32_t size;   /* size within the grant */
> +#define GNTTAB_CACHE_CLEAN      (1<<0)
> +#define GNTTAB_CACHE_INVAL      (1<<1)
> +    uint32_t op;
> +};
> +DEFINE_GUEST_HANDLE_STRUCT(gnttab_cache_flush);
> +
> +/*
>   * Bitfield values for update_pin_status.flags.
>   */
>   /* Map the grant entry for access by I/O devices. */

If the ARM bits are correct, have a

Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>

for the common header.

David


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