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Re: [Xen-devel] [PATCH v2] tools: libxc: flush data cache after loading images into guest memory



On Thu, 2013-12-12 at 14:45 +0000, Stefano Stabellini wrote:
> On Thu, 12 Dec 2013, Ian Campbell wrote:
> > On Thu, 2013-12-12 at 14:30 +0000, Stefano Stabellini wrote:
> > > On Thu, 12 Dec 2013, 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>
> > > 
> > > Looks good to me
> > 
> > Is that an Ack?
> 
> Yep, but keep in mind that I don't maintain libxc :)

An Ack from an ARM side person is still useful IMHO, since that's where
the bulk of the actual functionality is.

Ian.


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