Re: [Xen-devel] [PATCH] xen/hvc: If we use xen_raw_printk let it also work on HVM guests.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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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