linux-kernel - Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw

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Message-ID: <20130814001050.GA10492@phenom.dumpdata.com>
Date:	Tue, 13 Aug 2013 20:10:50 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ian Campbell <ian.campbell@...rix.com>
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw_printk let it
 also work on HVM guests.

On Tue, Aug 13, 2013 at 11:20:05PM +0100, Ian Campbell wrote:
> On Tue, 2013-08-13 at 21:59 +0100, Ian Campbell wrote:
> 
> > > What it should be is:
> > > > >  
> > > > >  void xen_raw_console_write(const char *str)
> > > > >  {
> > > > > -	dom0_write_console(0, str, strlen(str));
> > > > > +	if (!xen_domain())
> > > > > +		return;
> > > > > +
> > > > > +	if (xen_pv_domain())
> > >             xen_domain()
> > > 
> > > > > +		dom0_write_console(0, str, strlen(str));
> > > > > +	else if (xen_hvm_domain() || xen_cpuid_base()) {
> > >      
> > > 	else if (xen_cpuid_base()) {
> > > 
> > > > > +		/* The hyperpage has not been setup yet. */
> > > > > +		int i, len = strlen(str);
> > > > > +		for (i = 0; i < len; i++)
> > > > > +			 outb(str[i], 0xe9);
> > > > > +	}
> > > > >  }
> > > 
> > > And then that should adhere to what I wrote up.
> > 
> > I think it does too.
> 
> Except as Daniel notes in <520A7145.5010306@...ho.nsa.gov> for unrelated
> reasons:
> 
> >         HVM guests can still use the PV output - they just need to use the console
> >         write hypercall instead of the HVM I/O port. I would think that PVH guests
> >         would default to using the hypercall as it is more efficient (it takes a
> >         string rather than one character per write).
> >         
> >         Actually, checking... the console_io hypercall would need to be added to
> >         the hvm_hypercall{32,64}_table for an HVM guest to be able to use it; they
> >         currently must use the I/O port. I didn't check the PVH patches.
> 
> Or did you actually try this code and it worked?

The one I typed up above - no. The one I had sent - yes.

But with that above mentioned comment from Daniel I think it is still
worth trying to do dom0_write_console and if the hypercall returns -ENOSYS 
then fall back on 0xe9.

And lastly send an patch to make hypercall_io work under HVM.

> 
> Ian.
> 
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