Re: [PATCH v9 1/3] x86/tlb: introduce a flush HVM ASIDs flag

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Apr 09, 2020 at 01:54:40PM +0200, Jan Beulich wrote:
> On 06.04.2020 12:57, Roger Pau Monne wrote:
> > --- a/xen/arch/x86/mm/hap/hap.c
> > +++ b/xen/arch/x86/mm/hap/hap.c
> > @@ -118,7 +118,7 @@ int hap_track_dirty_vram(struct domain *d,
> >              p2m_change_type_range(d, begin_pfn, begin_pfn + nr,
> >                                    p2m_ram_rw, p2m_ram_logdirty);
> >  
> > -            flush_tlb_mask(d->dirty_cpumask);
> > +            hap_flush_tlb_mask(d->dirty_cpumask);
> >  
> >              memset(dirty_bitmap, 0xff, size); /* consider all pages dirty */
> >          }
> > @@ -205,7 +205,7 @@ static int hap_enable_log_dirty(struct domain *d, bool_t log_global)
> >           * to be read-only, or via hardware-assisted log-dirty.
> >           */
> >          p2m_change_entry_type_global(d, p2m_ram_rw, p2m_ram_logdirty);
> > -        flush_tlb_mask(d->dirty_cpumask);
> > +        hap_flush_tlb_mask(d->dirty_cpumask);
> >      }
> >      return 0;
> >  }
> > @@ -234,7 +234,7 @@ static void hap_clean_dirty_bitmap(struct domain *d)
> >       * be read-only, or via hardware-assisted log-dirty.
> >       */
> >      p2m_change_entry_type_global(d, p2m_ram_rw, p2m_ram_logdirty);
> > -    flush_tlb_mask(d->dirty_cpumask);
> > +    hap_flush_tlb_mask(d->dirty_cpumask);
> >  }
> >  
> >  /************************************************/
> > @@ -798,7 +798,7 @@ hap_write_p2m_entry(struct p2m_domain *p2m, unsigned long gfn, l1_pgentry_t *p,
> >  
> >      safe_write_pte(p, new);
> >      if ( old_flags & _PAGE_PRESENT )
> > -        flush_tlb_mask(d->dirty_cpumask);
> > +        hap_flush_tlb_mask(d->dirty_cpumask);
> >  
> >      paging_unlock(d);
> >  
> 
> Following up on my earlier mail about paging_log_dirty_range(), I'm
> now of the opinion that all of these flushes should go away too. I
> can only assume that they got put where they are when HAP code was
> cloned from the shadow one. These are only p2m operations, and hence
> p2m level TLB flushing is all that's needed here.

IIRC without those ASID flushes NPT won't work correctly, as I think
it relies on those flushes when updating the p2m.

We could see about moving those flushes inside the NPT functions that
modify the p2m, AFAICT p2m_pt_set_entry which calls
p2m->write_p2m_entry relies on the later doing the ASID flushes, as it
doesn't perform any.

Thanks, Roger.