Re: [Xen-devel] [PATCH RFC 2/2] xen: make available hvm_fep to non-debug build as well

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jun 16, 2016 at 05:37:03AM -0600, Jan Beulich wrote:
> >>> On 15.06.16 at 16:31, <wei.liu2@xxxxxxxxxx> wrote:
> > @@ -182,6 +181,32 @@ static int __init hvm_enable(void)
> >      if ( !opt_altp2m_enabled )
> >          hvm_funcs.altp2m_supported = 0;
> >  
> > +    if ( opt_hvm_fep )
> > +    {
> > +        unsigned i, j;
> 
> unsigned int
> 

Ack.

> > +        printk("**********************************************\n");
> > +        printk("******* WARNING: HVM FORCED EMULATION PREFIX IS 
> > PERMITTED\n");
> > +        printk("******* This option is *ONLY* intended to aid debugging "
> > +               "and testing of Xen\n");
> > +        printk("******* that HVM guest can enter instruction emulator "
> > +               "with UD instruction.\n");
> > +        printk("******* It has implication on the security of the 
> > system.\n");
> > +        printk("******* Please *DO NOT* use this in production.\n");
> > +        printk("**********************************************\n");
> > +        add_taint(TAINT_HVM_FEP);
> 
> Should we perhaps taint the system only the first time a guest
> makes use of this?
> 

Doesn't that add overhead to a potential hot path? Arguably it is only
setting a bit in a flag, but still...

> > +        for ( i = 0; i < 3; i++ )
> > +        {
> > +            printk("%d... ", 3-i);
> 
> %u and spaces around - please.
> 

Ack.

Wei.

> Jan
> 

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