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

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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.

> 
> 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.

> +|                                    |                                   |
> +|   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 :)




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