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

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Message-ID: <1376427570.9273.39.camel@hastur.hellion.org.uk>
Date:	Tue, 13 Aug 2013 21:59:30 +0100
From:	Ian Campbell <ian.campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw_printk let it
 also work on HVM guests.

On Tue, 2013-08-13 at 16:53 -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 13, 2013 at 09:31:44PM +0100, Ian Campbell wrote:
> > On Fri, 2013-08-09 at 10:55 -0400, Konrad Rzeszutek Wilk wrote:
> > > The xen_raw_printk works great for debugging purposes and for
> > > it print anything the Xen hypervisor has to be built with 'debug=y'.
> > > 
> > > As such there is no difference between a PV or an PVHVM guest
> > > using the hypercall, so lets use it.
> > >
> > > Lastly if the hyper-page is not setup yet (for example during
> > > early HVM boot), then use the 0xe9 port if it has detected
> > > that it is running under an Xen hypervisor.
> > 
> > Does this really do what you say?
> > 
> > I think xen_pv_domain returns false for a PVHVM guest, meaning that we
> > only use the hypercall for proper PV guests and for PVHVM we use port
> > 0xe9 until the hypercall page is setup at which point we silently
> > discard any attempt to print via this mechanism.
> > 
> 
> 'via this mechanism' refers to 0xe9 or dom0_write_console?

Neither, I meant the xen_raw_console_write mechanism.

> 
> > or am I reading it wrong?
> 
> The code did have a bug as it would on HVM (after the hyper-page
> was setup) still use 0xe9 instead of the dom0_write_console.
> 
> 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.

> Thanks for pointing this out!

NP!

Ian.


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