Re: [PATCH v3 3/5] arch/x86/mm: Refactor cond_ibpb() to support other use cases

[Singh, Balbir]

On Fri, 2020-04-17 at 15:07 +0200, Thomas Gleixner wrote:
> 
> Balbir Singh <sblbir@xxxxxxxxxx> writes:
> > 
> >  /*
> > - * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is
> > - * stored in cpu_tlb_state.last_user_mm_ibpb.
> > + * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is
> > + * stored in cpu_tlb_state.last_user_mm_spec.
> >   */
> >  #define LAST_USER_MM_IBPB    0x1UL
> > +#define LAST_USER_MM_SPEC_MASK       (LAST_USER_MM_IBPB)
> > 
> >       /* Reinitialize tlbstate. */
> > -     this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, LAST_USER_MM_IBPB);
> > +     this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_IBPB);
> 
> Shouldn't that be LAST_USER_MM_MASK?
> 
> 

No, that crashes the system for SW flushes, because it tries to flush the L1D
via the software loop and early enough we don't have the l1d_flush_pages
allocated. LAST_USER_MM_MASK has LAST_USER_MM_FLUSH_L1D bit set.

Balbir Singh.