Re: [Xen-devel] [PATCH] tools: libxc: flush data cache after loading images into guest memory

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 12/12/2013 12:21 PM, Ian Campbell wrote:
> On ARM guest OSes are started with MMU and Caches disables (as they are on
> native) however caching is enabled in the domain running the builder and
> therefore we must flush the cache as we load the blobs, otherwise when the
> guest starts running it may not see them. The dom0 build in the hypervisor has
> the same requirements and already does the right thing.
>
> The mechanism for performing a cache flush from userspace is OS specific, so
> implement this as a new osdep hook:
>
>   - On 32-bit ARM Linux provides a system call to flush the cache.
>   - On 64-bit ARM Linux the processor is configured to allow cache flushes
>     directly from userspace.
>   - Non-Linux platforms will need to provide their own implementation. If
>     similar mechanisms are not available then a new privcmd ioctl should be a
>     suitable alternative.
>
> No cache maintenance is required on x86, so provide a stub for all non-Linux
> platforms which returns success on x86 only and log an error otherwise.
>
> This fixes guest building on Xgene which has a very large L3 cache and so is
> particularly susceptible to this problem. It has also been observed
> sporadically on midway.
>
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Andre Przywara <andre.przywara@xxxxxxxxxxx>
> Cc: Pranavkumar Sawargaonkar <psawargaonkar@xxxxxxx>
> Cc: Anup Patel <apatel@xxxxxxx>
> ---
> Freeze: Bugfix.
> ---
>   tools/libxc/xc_dom_armzimageloader.c |    1 +
>   tools/libxc/xc_dom_binloader.c       |    1 +
>   tools/libxc/xc_dom_core.c            |    2 ++
>   tools/libxc/xc_linux_osdep.c         |   39 ++++++++++++++++++++++++++++++++++
>   tools/libxc/xc_minios.c              |   11 ++++++++++
>   tools/libxc/xc_netbsd.c              |   12 +++++++++++
>   tools/libxc/xc_private.c             |    5 +++++
>   tools/libxc/xc_private.h             |    3 +++
>   tools/libxc/xc_solaris.c             |   12 +++++++++++
>   tools/libxc/xenctrl_osdep_ENOSYS.c   |    6 ++++++
>   tools/libxc/xenctrlosdep.h           |    1 +
>   11 files changed, 93 insertions(+)

[..]


> diff --git a/tools/libxc/xenctrl_osdep_ENOSYS.c 
> b/tools/libxc/xenctrl_osdep_ENOSYS.c
> index 4821342..c6fceff 100644
> --- a/tools/libxc/xenctrl_osdep_ENOSYS.c
> +++ b/tools/libxc/xenctrl_osdep_ENOSYS.c
> @@ -63,6 +63,10 @@ static void *ENOSYS_privcmd_map_foreign_ranges(xc_interface 
> *xch, xc_osdep_handl
>       return MAP_FAILED;
>   }
>
> +static void ENOSYS_privcmd_cache_flush(xc_interface *xch, const void *p, 
> size_t n)
> +{
> +}
> +
Missing IPRINTF for this function.

>   static struct xc_osdep_ops ENOSYS_privcmd_ops =
>   {
>       .open      = &ENOSYS_privcmd_open,
> @@ -74,6 +78,8 @@ static struct xc_osdep_ops ENOSYS_privcmd_ops =
>           .map_foreign_bulk = &ENOSYS_privcmd_map_foreign_bulk,
>           .map_foreign_range = &ENOSYS_privcmd_map_foreign_range,
>           .map_foreign_ranges = &ENOSYS_privcmd_map_foreign_ranges,
> +
> +        .cache_flush = &ENOSYS_privcmd_cache_flush,
>       }
>   };
>
> diff --git a/tools/libxc/xenctrlosdep.h b/tools/libxc/xenctrlosdep.h
> index e610a24..6c9a005 100644
> --- a/tools/libxc/xenctrlosdep.h
> +++ b/tools/libxc/xenctrlosdep.h
> @@ -89,6 +89,7 @@ struct xc_osdep_ops
>               void *(*map_foreign_ranges)(xc_interface *xch, xc_osdep_handle h, 
> uint32_t dom, size_t size, int prot,
>                                           size_t chunksize, 
> privcmd_mmap_entry_t entries[],
>                                           int nentries);
> +            void (*cache_flush)(xc_interface *xch, const void *p, size_t n);
>           } privcmd;
>           struct {
>               int (*fd)(xc_evtchn *xce, xc_osdep_handle h);
--
Julien Grall

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