Re: [Xen-devel] [PATCH 08/18] arm/altp2m: Add HVMOP_altp2m_destroy_p2m.

[Julien Grall <julien.grall@xxxxxxx>]

On 05/07/16 12:37, Sergej Proskurin wrote:
> On 07/04/2016 06:32 PM, Julien Grall wrote:
> > Hello Sergej,
> >
> > On 04/07/16 12:45, Sergej Proskurin wrote:
> > > Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
> > > ---
> > > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > Cc: Julien Grall <julien.grall@xxxxxxx>
> > > ---
> > >    xen/arch/arm/hvm.c        |  2 +-
> > >    xen/arch/arm/p2m.c        | 32 ++++++++++++++++++++++++++++++++
> > >    xen/include/asm-arm/p2m.h |  3 +++
> > >    3 files changed, 36 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
> > > index 005d7c6..f4ec5cf 100644
> > > --- a/xen/arch/arm/hvm.c
> > > +++ b/xen/arch/arm/hvm.c
> > > @@ -145,7 +145,7 @@ static int
> > > do_altp2m_op(XEN_GUEST_HANDLE_PARAM(void) arg)
> > >            break;
> > >
> > >        case HVMOP_altp2m_destroy_p2m:
> > > -        rc = -EOPNOTSUPP;
> > > +        rc = p2m_destroy_altp2m_by_id(d, a.u.view.view);
> > >            break;
> > >
> > >        case HVMOP_altp2m_switch_p2m:
> > > diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> > > index 6c41b98..f82f1ea 100644
> > > --- a/xen/arch/arm/p2m.c
> > > +++ b/xen/arch/arm/p2m.c
> > > @@ -2200,6 +2200,38 @@ void p2m_flush_altp2m(struct domain *d)
> > >        altp2m_unlock(d);
> > >    }
> > >
> > > +int p2m_destroy_altp2m_by_id(struct domain *d, unsigned int idx)
> > > +{
> > > +    struct p2m_domain *p2m;
> > > +    int rc = -EBUSY;
> > > +
> > > +    if ( !idx || idx >= MAX_ALTP2M )
> > Can you please add a comment to explain why the altp2m at index 0
> > cannot be destroyed.
> This has been adopted from the x86 implementation. The altp2m[0] is
> considered as hostp2m and is used as a safe harbor to which you can
> switch as long as altp2m is active. After deactivating altp2m, the
> system switches back to the original hostp2m view.That is, altp2m[0]
> should only be destroyed/flushed/freed, when altp2m is deactivated.
Please add a comment in the code to explain it.

Regards,

--
Julien Grall

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