[MODERATED] Re: [PATCH v4 03/10] TAAv4 3

On Wed, Sep 25, 2019 at 06:13:05PM -0700, speck for Pawan Gupta wrote:
> > > > > +static int __init tsx_cmdline(char *str)
> > > > > +{
> > > > > +	if (!str)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	if (!strcmp(str, "on"))
> > > > > +		tsx_ctrl_state = TSX_CTRL_ENABLE;
> > > > > +	else if (!strcmp(str, "off"))
> > > > > +		tsx_ctrl_state = TSX_CTRL_DISABLE;
> > > > > +
> > > > > +	return 0;
> > > > > +}
> > > > > +early_param("tsx", tsx_cmdline);
> > > > 
> > > > Hmm...  Let's say I have a non-TSX system.  I specify tsx=on.  This will
> > > > set tsx_ctrl_state=TSX_CTRL_ENABLE, then tsx_ctrl_check_support() will
> > > > set it to tsx_ctrl_state=TSX_CTRL_NOT_SUPPORTED.
> > > > 
> > > > I *think* this all works, but I'd love a comment or two about it.  Maybe
> > > > even something that makes it clear that tsx_en/disable() are both only
> > > > called when TSX *AND* TSX_CTRL_MSR are supported.
> > > > 
> > > > This is all kinda weird and confusing because we're doing this all
> > > > without the X86_FEATURE bits for TSX.
> > > 
> > > If we add another X86_FEATURE bit it will have exact same state as
> > > X86_FEATURE_RTM.  Do we really need this?
> > 
> > How about moving the tsx_init() call to early_init_intel()?  Then you'd
> > be able to check the feature bit above.  And that might make the
> > ordering a little easier to follow.
> 
> Sorry, I am failing to understand how it would make a difference.
> early_init_intel() is also called from init_init().

Regardless, shouldn't tsx_init() at least be called before
cpu_set_bug_bits(), so that X86_BUG_TAA can get set appropriately?

In that case, instead of early_param(), tsx_init() could just use
cmdline_find_option() to find the 'tsx=' option.  That would also have
the advantage of making it much easier to untangle the initialization
order.

If early_init_intel() isn't the right spot, then maybe
early_identify_cpu().

-- 
Josh