Re: [PATCHv2] x86/alternatives: Disable KASAN in apply_alternatives()

[Peter Zijlstra]

On Wed, Oct 11, 2023 at 10:11:46AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > >  	DPRINTK(ALT, "alt table %px, -> %px", start, end);
> > > +
> > > +	/*
> > > +	 * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
> > > +	 * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
> > > +	 * During the process, KASAN becomes confused and triggers
> > 
> > 	because of partial LA57 convertion ..
> 
> Not all LA57 related sites are patched yet at this point, and KASAN sees
> a weird & broken mixture of LA48 and LA57 runtime semantics, right?
> 
> Ie. as far as KASAN is concerned, the LA48 -> LA57 behavioral switchover
> must be atomic, but during the kernel code patching process it isn't.

Yep, half-way through the patching it observes inconsistencies and goes
WTF :-)