Re: [PATCH 3/4] x86/tsx: Clear CPUID bits when TSX always force aborts

[Pawan Gupta]

On 11.06.2021 12:03, Borislav Petkov wrote:
> On Wed, Jun 09, 2021 at 02:13:38PM -0700, Pawan Gupta wrote:
> > @@ -114,6 +127,26 @@ void __init tsx_init(void)
> >  			tsx_ctrl_state = TSX_CTRL_ENABLE;
> >  	}
> >
> > +	/*
> > +	 * Hardware will always abort a TSX transaction if both CPUID bits
> > +	 * RTM_ALWAYS_ABORT and TSX_FORCE_ABORT are enumerated.  In this case it
> > +	 * is better not to enumerate CPUID.RTM and CPUID.HLE bits. Clear them
> > +	 * here.
> > +	 */
> > +	if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) &&
> > +	    boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
> > +		tsx_ctrl_state = TSX_CTRL_RTM_ALWAYS_ABORT;
> > +		tsx_clear_cpuid();
> > +		setup_clear_cpu_cap(X86_FEATURE_RTM);
> > +		setup_clear_cpu_cap(X86_FEATURE_HLE);
> > +		return;
> > +	}
>
> Why isn't this happening as the first thing on entry in that tsx_init()
> function? IOW, there's no point to noodle through cmdline options etc if
> the hardware will always abort transactions.

Because the next patch is adding tsx=fake cmdline, for that this code
needs to be executed after cmdline parsing. I wanted to avoid the churn
to move this code between patches.

But, I see your comment for 4/4 i.e. tsx=fake may not be needed. It was
added after an internal test failure.

tsx=fake is really for a corner case and if that patch goes away it
would make sense to move the code in question here before cmdline
parsing.

Thanks,
Pawan