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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.06.16 at 13:52, <wei.liu2@xxxxxxxxxx> wrote:
> On Thu, Jun 16, 2016 at 05:37:03AM -0600, Jan Beulich wrote:
>> >>> On 15.06.16 at 16:31, <wei.liu2@xxxxxxxxxx> wrote:
>> > +        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...

How can that be a hot path, if it's not even usable without the
option set?

Jan


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