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 01:12:34PM +0100, Andrew Cooper wrote:
> On 16/06/16 12:52, Wei Liu wrote:
> >
> >>> +        printk("**********************************************\n");
> >>> +        printk("******* WARNING: HVM FORCED EMULATION PREFIX IS 
> >>> PERMITTED\n");
> 
> I would say "available" rather than permitted in this case.
> 
> >>> +        printk("******* This option is *ONLY* intended to aid debugging "
> >>> +               "and testing of Xen\n");
> 
> Despite the line length, I would keep this string on a single line.  If
> you want it a little shorter, you can drop "debugging and", leaving just
> testing.
> 
> >>> +        printk("******* that HVM guest can enter instruction emulator "
> >>> +               "with UD instruction.\n");
> 
> I think this like isn't necessary.  Anyone who is unclear what FEP is
> can look it up.
> 
> >>> +        printk("******* It has implication on the security of the 
> >>> system.\n");
> 
> implications.
> 

All fixed.

> >>> +        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...
> 
> FEP is not a fastpath at all.  It would be fine to defer to
> hvm_ud_intercept().
> 

NP.

Wei.

> ~Andrew

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