Re: [PATCH v2 21/27] docs: kvm: Convert locking.txt to ReST format

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Em Fri, 7 Feb 2020 09:48:03 +0100
Cornelia Huck <cohuck@xxxxxxxxxx> escreveu:

> On Fri, 7 Feb 2020 07:24:09 +0100
> Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> wrote:
> 
> > >     
> > > > 
> > > > Would be nicer but this is acceptable too I think.  Especially, the
> > > > monospaced font allows breaking the table and keeping the parts aligned.      
> > 
> > I couldn't resist trying to use a table ;-)
> > 
> > The following patch does that. IMO, it looks nice on both text and html
> > outputs.  
> 
> Now that I see this, I think this version is actually more readable
> than the existing text.

Yes, that was my feeling too: even for one reading the text version,
it looked clearer on my eyes.

> 
> > 
> > Cheers,
> > Mauro
> > 
> > diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst
> > index 428cb3412ecc..c02291beac3f 100644
> > --- a/Documentation/virt/kvm/locking.rst
> > +++ b/Documentation/virt/kvm/locking.rst
> > @@ -59,30 +59,39 @@ The mapping from gfn to pfn may be changed since we can only ensure the pfn
> >  is not changed during cmpxchg. This is a ABA problem, for example, below case
> >  will happen:
> >  
> > -At the beginning::
> > -
> > -	gpte = gfn1
> > -	gfn1 is mapped to pfn1 on host
> > -	spte is the shadow page table entry corresponding with gpte and
> > -	spte = pfn1
> > -
> > -	   VCPU 0                           VCPU0
> > -
> > -on fast page fault path::
> > -
> > -   old_spte = *spte;
> > -                                 pfn1 is swapped out:
> > -                                    spte = 0;
> > -
> > -                                 pfn1 is re-alloced for gfn2.
> > -
> > -                                 gpte is changed to point to
> > -                                 gfn2 by the guest:
> > -                                    spte = pfn1;
> > -
> > -   if (cmpxchg(spte, old_spte, old_spte+W)
> > -	mark_page_dirty(vcpu->kvm, gfn1)
> > -             OOPS!!!
> > ++------------------------------------------------------------------------+
> > +| At the beginning::                                                     |
> > +|                                                                        |
> > +|	gpte = gfn1                                                      |
> > +|	gfn1 is mapped to pfn1 on host                                   |
> > +|	spte is the shadow page table entry corresponding with gpte and  |
> > +|	spte = pfn1                                                      |
> > ++------------------------------------------------------------------------+
> > +| On fast page fault path:                                               |
> > ++------------------------------------+-----------------------------------+
> > +| CPU 0:                             | CPU 1:                            |
> > ++------------------------------------+-----------------------------------+
> > +| ::                                 |                                   |  
> 
> The '::' directives look a bit like leftover christmas decorations,
> but it's not really distracting, and on the plus side, we'll get nice
> html formatting.

Yes the only downside are those extra "::". The alternatives to it that
would produce a similar look and feel would be a lot worse.

> 
> > +|                                    |                                   |
> > +|   old_spte = *spte;                |                                   |
> > ++------------------------------------+-----------------------------------+
> > +|                                    | pfn1 is swapped out::             |
> > +|                                    |                                   |
> > +|                                    |    spte = 0;                      |
> > +|                                    |                                   |
> > +|                                    | pfn1 is re-alloced for gfn2.      |
> > +|                                    |                                   |
> > +|                                    | gpte is changed to point to       |
> > +|                                    | gfn2 by the guest::               |
> > +|                                    |                                   |
> > +|                                    |    spte = pfn1;                   |
> > ++------------------------------------+-----------------------------------+
> > +| ::                                                                     |
> > +|                                                                        |
> > +|   if (cmpxchg(spte, old_spte, old_spte+W)                              |
> > +|	mark_page_dirty(vcpu->kvm, gfn1)                                 |
> > +|            OOPS!!!                                                     |
> > ++------------------------------------------------------------------------+
> >  
> >  We dirty-log for gfn1, that means gfn2 is lost in dirty-bitmap.
> >    
> 
> So I'd like to cast my vote for this version :)
> 

Ok. I'm submitting version 3 with this version.

Regards,
Mauro

Cheers,
Mauro



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