Re: [Qemu-ppc] [Qemu-devel] [PATCH 3/3] target/ppc: filter out non-zero PCR values when using TCG

[Greg Kurz]

On Fri, 15 Jun 2018 11:45:01 +1000
David Gibson <address@hidden> wrote:

> On Fri, Jun 15, 2018 at 12:00:20AM +0200, Greg Kurz wrote:
> > On Thu, 14 Jun 2018 09:52:55 -1000
> > Richard Henderson <address@hidden> wrote:
> >   
> > > On 06/12/2018 10:19 PM, Greg Kurz wrote:  
> > > > I'm confused... I don't see anything related to HTM in TCG. Also we have
> > > > the following in cap_htm_apply():
> > > > 
> > > >     if (tcg_enabled()) {
> > > >         error_setg(errp,
> > > >                    "No Transactional Memory support in TCG, try 
> > > > cap-htm=off");
> > > > 
> > > > I'm probably missing something... can you enlighten me ?    
> > > 
> > > One of the two IBM machines -- and I thought it was ppc not s390x, but 
> > > the code
> > > you quote seems to deny that memory -- has stub support for TM within 
> > > TCG.  
> > 
> > Oh ? I didn't know and didn't check :)  
> 
> That is true, there are stub implementations of the TM instructions.
> 
> >   
> > > To wit, the instructions are recognized and transactions always fail.  
> > > Which is
> > > not a bad way to test the required fallback paths that rarely fail on 
> > > hardware.
> > >  ;-)  
> > 
> > If TM instructions don't cause an exception, I guess its reasonable to say
> > they're supported :)  
> 
> That argument has come up before, and I disagree.  I don't think it's
> reasonable to advertise TM support as available if the instructions
> always fail.
> 

Fair enough! :)

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