Re: [Xen-devel] [PATCH v2 3/4] xen/arm: clean and invalidate all guest caches by VMID after domain build.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.02.14 at 15:22, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
> --- a/tools/libxc/xc_dom_boot.c
> +++ b/tools/libxc/xc_dom_boot.c
> @@ -351,6 +351,10 @@ int xc_dom_gnttab_seed(xc_interface *xch, domid_t domid,
>          return -1;
>      }
>  
> +    /* Guest shouldn't really touch its grant table until it has
> +     * enabled its caches. But lets be nice. */
> +    xc_domain_cacheflush(xch, domid, gnttab_gmfn, gnttab_gmfn + 1);

Looking at this and further similar code I think it would be cleaner
for the xc interface to take a start MFN and a count, and for the
hypervisor interface to use an inclusive range (such that overflow
is not a problem).

> --- a/xen/include/asm-x86/page.h
> +++ b/xen/include/asm-x86/page.h
> @@ -346,6 +346,9 @@ static inline uint32_t cacheattr_to_pte_flags(uint32_t 
> cacheattr)
>      return ((cacheattr & 4) << 5) | ((cacheattr & 3) << 3);
>  }
>  
> +/* No cache maintenance required on x86 architecture. */
> +static inline void cacheflush_page(unsigned long mfn) {}

The function name is certainly sub-optimal: If I needed a page-range
cache flush and found a function named like this, I'd assume it does
what its name says - flush the page from the cache. sync_page() or
some such may be better suited to express that this is something
that may be a no-op on certain architectures.

Jan


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