Re: [Xen-devel] [PATCH 19/22] xen/arm: p2m: Inline p2m_load_VTTBR into p2m_restore_state

[Julien Grall <julien.grall@xxxxxxx>]

On 22/07/16 09:07, Sergej Proskurin wrote:
> Hi Julien,
Hello Sergej,

> On 07/20/2016 06:11 PM, Julien Grall wrote:
> > p2m_restore_state is the last caller of p2m_load_VTTBR and already check
> > if the vCPU does not belong to the idle domain.
> >
> > Note that it is likely possible to remove some isb in the function
> > p2m_restore_state, however this is not the purpose of this patch. So the
> > numerous isb have been left.
> Right now, I don't see any issues with removing the p2m_load_VTTBR
> function in combination with changes applied to flush_tlb_domain in your
> patch #18 and #17. However, I am not entirely sure whether it makes
> sense to entirely remove the function and replicate the VTTBR loading
> functionality across multiple functions. Why don't we just provide a
> struct p2m_domain* to p2m_load_VTTBR (potentially with a backpointer to
> the associated domain, as it is shown in the arm/altp2m patch) and use
> the function inline?
Because ideally this function should take a p2m in parameter and a p2m 
cannot belong to an idle domain. So the function would be:
WRITE_SYSREG64(p2m->vttbr, VTTBR_EL2);
isb();

However, in the case of p2m_restore_state the isb() is not necessary and 
will impact the performance. Yes, I know the function contains a lots of 
pointless isb(), this needs to be fixed at some point.
So overall, this function is not necessary.

Regards,

--
Julien Grall

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