linux-kernel - Re: [PATCH v5 05/13] xen/arm,arm64: move Xen initialization earlier

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Message-ID: <1378457939.14745.73.camel@kazak.uk.xensource.com>
Date:	Fri, 6 Sep 2013 09:58:59 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	Catalin Marinas <catalin.marinas@....com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>
Subject: Re: [PATCH v5 05/13] xen/arm,arm64: move Xen initialization earlier

On Thu, 2013-09-05 at 17:59 +0100, Stefano Stabellini wrote:
> On Thu, 5 Sep 2013, Catalin Marinas wrote:
> > On Thu, Aug 29, 2013 at 07:32:26PM +0100, Stefano Stabellini wrote:
> > > Move Xen initialization earlier, before any DMA requests can be made.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > 
> > I guess you should cc the corresponding maintainers here.
> 
> Thanks for the reminder, I'll do that.
> 
> 
> > >  arch/arm/include/asm/xen/hypervisor.h |    8 ++++++++
> > >  arch/arm/kernel/setup.c               |    2 ++
> > >  arch/arm/xen/enlighten.c              |   21 ++++++++++++++-------
> > >  arch/arm64/kernel/setup.c             |    2 ++
> > >  4 files changed, 26 insertions(+), 7 deletions(-)
> > 
> > [...]
> > 
> > > --- a/arch/arm64/kernel/setup.c
> > > +++ b/arch/arm64/kernel/setup.c
> > > @@ -53,6 +53,7 @@
> > >  #include <asm/traps.h>
> > >  #include <asm/memblock.h>
> > >  #include <asm/psci.h>
> > > +#include <asm/xen/hypervisor.h>
> > >  
> > >  unsigned int processor_id;
> > >  EXPORT_SYMBOL(processor_id);
> > > @@ -267,6 +268,7 @@ void __init setup_arch(char **cmdline_p)
> > >  	unflatten_device_tree();
> > >  
> > >  	psci_init();
> > > +	xen_early_init();
> > 
> > So Xen guests don't have any hope for single Image? Basically you set
> > dma_ops unconditionally in xen_early_init(), even if the kernel is not
> > intended to run under Xen.
> 
> That should not happen: if we are not running on Xen xen_early_init
> returns early, before calling xen_mm_init.

x96 has a call to init_hypervisor_platform() at approximately this
location, which detects and calls the init function for any of Xen, KVM,
hyperv and vmware. I guess only Xen and KVM are currently relevant on
Linux ARM(64), so perhaps adding similar infrastructure on ARM would be
overkill at this point. I don't know if KVM needs such an early C-land
hook, I suppose it needs it even earlier so it can set up the hyp mode
trampoline from head.S?

Ian.

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