Re: [Xen-devel] [RFC 21/22] xen/arm: p2m: Re-implement p2m_set_mem_access using p2m_{set, get}_entry

[Mark Rutland <mark.rutland@xxxxxxx>]

Hi,

I realised I made a confusing mistake in my last reply; clarification below.

On Mon, Aug 01, 2016 at 06:26:54PM +0100, Mark Rutland wrote:
> On Mon, Aug 01, 2016 at 05:57:50PM +0100, Julien Grall wrote:
> > however we only need one TLBI instruction (assuming there is
> > no superpage shattering) per-batch rather than one per-entry in this
> > case.
> 
> I got Cc'd to a reply without the original patch context, so I'm not
> sure what the case is here. I'm not exactly sure what you mean by
> "per-batch".
> 
> Assuming that you've (only) changed the permissions (i.e. the AP bits
> and XN bits) of a number of stage-2 leaf entries, you need either:

[...]

> * Per entry, a TLBI IPAS2LE1IS
> 
>   e.g. 
> 
>     for_each_entry(x)
>       modify_ap_bits(x);
>     dsb(ishst);
>     tlbi(ipas2le1is);
>     dsb(ish);

Here I was trying to have the bare minimum barriers necessary, but in focussing
on that I failed to add the required loop to have a TLBI per entry.

The above should have been:

  for_each_entry(x)
    modify_ap_bits(x);
  dsb(ishst);
  for_each_entry(x)
    tlbi(ipas2le1is, x);
  dsb(ish);

Assuming the necessary bit fiddling for the TLBI to affect the IPA of x, with
the right VMID, etc.

Thanks,
Mark.

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