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 20:10 -0400, Konrad Rzeszutek Wilk wrote:
> 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@xxxxxxxxxxxxx> 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.

So you didn't try under PVHVM? That's what I was asking when I asked if
you tried it, since that is the point of this patch.

Ian.

Ian.


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