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RE: [PATCH] xen/arm: Reduce redundant clear root pages when teardown p2m
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Mon, 12 Dec 2022 11:27:26 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Mon, 12 Dec 2022 11:27:46 +0000
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- Thread-topic: [PATCH] xen/arm: Reduce redundant clear root pages when teardown p2m
Hi Julien,
> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Subject: Re: [PATCH] xen/arm: Reduce redundant clear root pages when
> teardown p2m
>
> Hi Henry,
>
> > PROGRESS(p2m):
> > + /*
> > + * We are about to free the intermediate page-tables, so clear the
> > + * root to prevent any walk to use them.
> > + */
> > + p2m_clear_root_pages(&d->arch.p2m);
>
> The commit message suggests this should only be called once. However,
> you will still end up to call p2m_clear_root_pages() multiple time if
> p2m_teardown() is preempted.
Thanks for confirming this, would adding another PROGRESS stage
such as PROGRESS(p2m_clean) before PROGRESS(p2m) seem ok to you?
>
> > ret = p2m_teardown(d, true);
> > if ( ret )
> > return ret;
> > diff --git a/xen/arch/arm/include/asm/p2m.h
> b/xen/arch/arm/include/asm/p2m.h
> > index 91df922e1c..bf5183e53a 100644
> > --- a/xen/arch/arm/include/asm/p2m.h
> > +++ b/xen/arch/arm/include/asm/p2m.h
> > @@ -281,6 +281,7 @@ int p2m_set_entry(struct p2m_domain *p2m,
> >
> > bool p2m_resolve_translation_fault(struct domain *d, gfn_t gfn);
> >
> > +void p2m_clear_root_pages(struct p2m_domain *p2m);
> > void p2m_invalidate_root(struct p2m_domain *p2m);
> >
> > /*
> > diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> > index 948f199d84..0c942c5923 100644
> > --- a/xen/arch/arm/p2m.c
> > +++ b/xen/arch/arm/p2m.c
> > @@ -1314,6 +1314,18 @@ static void p2m_invalidate_table(struct
> p2m_domain *p2m, mfn_t mfn)
> > p2m->need_flush = true;
> > }
> >
> > /*
> > * The domain will not be scheduled anymore, so in theory we should
> > * not need to flush the TLBs. Do it for safety purpose.
>
> This flush needs to be moved in p2m_clear_root_pages().
Sure, will move this in v2.
Kind regards,
Henry
>
> Cheers,
>
> --
> Julien Grall
|
