linux-kernel - Re: [PATCH v9] xen/grant-table: Avoid m2p

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Thu, 20 Feb 2014 18:26:53 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Zoltan Kiss <zoltan.kiss@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: [PATCH v9] xen/grant-table: Avoid m2p_override during mapping

On Thu, 20 Feb 2014, David Vrabel wrote:
> On 20/02/14 18:17, Stefano Stabellini wrote:
> > On Thu, 20 Feb 2014, Zoltan Kiss wrote:
> >> On 20/02/14 17:26, Stefano Stabellini wrote:
> >>> On Mon, 17 Feb 2014, Zoltan Kiss wrote:
> >>>> On 16/02/14 18:36, Stefano Stabellini wrote:
> >>>>> On Wed, 12 Feb 2014, Zoltan Kiss wrote:
> >>>>>> diff --git a/arch/arm/include/asm/xen/page.h
> >>>>>> b/arch/arm/include/asm/xen/page.h
> >>>>>> index e0965ab..4eaeb3f 100644
> >>>>>> --- a/arch/arm/include/asm/xen/page.h
> >>>>>> +++ b/arch/arm/include/asm/xen/page.h
> >>>>>> @@ -97,16 +97,15 @@ static inline pte_t *lookup_address(unsigned long
> >>>>>> address, unsigned int *level)
> >>>>>>    	return NULL;
> >>>>>>    }
> >>>>>>
> >>>>>> -static inline int m2p_add_override(unsigned long mfn, struct page
> >>>>>> *page,
> >>>>>> -		struct gnttab_map_grant_ref *kmap_op)
> >>>>>> -{
> >>>>>> -	return 0;
> >>>>>> -}
> >>>>>> -
> >>>>>> -static inline int m2p_remove_override(struct page *page, bool
> >>>>>> clear_pte)
> >>>>>> -{
> >>>>>> -	return 0;
> >>>>>> -}
> >>>>>> +extern int set_foreign_p2m_mapping(struct gnttab_map_grant_ref
> >>>>>> *map_ops,
> >>>>>> +				   struct gnttab_map_grant_ref
> >>>>>> *kmap_ops,
> >>>>>> +				   struct page **pages, unsigned int
> >>>>>> count,
> >>>>>> +				   bool m2p_override);
> >>>>>> +
> >>>>>> +extern int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref
> >>>>>> *unmap_ops,
> >>>>>> +				     struct gnttab_map_grant_ref
> >>>>>> *kmap_ops,
> >>>>>> +				     struct page **pages, unsigned int
> >>>>>> count,
> >>>>>> +				     bool m2p_override);
> >>>>>
> >>>>> Much much better.
> >>>>> The only comment I have is about this m2p_override boolean parameter.
> >>>>> m2p_override is now meaningless in this context, what we really want to
> >>>>> let the arch specific implementation know is whether the mapping is a
> >>>>> kernel only mapping or a userspace mapping.
> >>>>> Testing for kmap_ops != NULL might even be enough, but it would not
> >>>>> improve the interface.
> >>>> gntdev is the only user of this, the kmap_ops parameter there is:
> >>>> use_ptemod ? map->kmap_ops + offset : NULL
> >>>> where:
> >>>> use_ptemod = !xen_feature(XENFEAT_auto_translated_physmap);
> >>>> So I think we can't rely on kmap_ops to decide whether we should
> >>>> m2p_override
> >>>> or not.
> >>>>
> >>>>> Is it possible to realize if the mapping is a userspace mapping by
> >>>>> checking for GNTMAP_application_map in map_ops?
> >>>>> Otherwise I would keep the boolean and rename it to user_mapping.
> >>>> Sounds better, but as far as I see gntdev set that flag in
> >>>> find_grant_ptes,
> >>>> which is called only
> >>>>
> >>>> if (use_ptemod) {
> >>>> 	err = apply_to_page_range(vma->vm_mm, vma->vm_start,
> >>>> 				  vma->vm_end - vma->vm_start,
> >>>> 				  find_grant_ptes, map);
> >>>>
> >>>> So if xen_feature(XENFEAT_auto_translated_physmap), we don't have
> >>>> kmap_ops,
> >>>> and GNTMAP_application_map is not set as well, but I guess we still need
> >>>> m2p_override. Or not? I'm a bit confused, maybe because of Monday ...
> >>>
> >>> If xen_feature(XENFEAT_auto_translated_physmap) we shouldn't need the
> >>> m2p_override.
> >>>
> >>
> >> So it's safe to assume that we need m2p_override only if kmap_ops != NULL, and
> >> we can avoid the extra bool parameter, is that correct? At least with the
> >> current users of grant mapping it seems to be true.
> >> In which case we don't need the wrappers for gnttab_[un]map_refs as well.
> >> Actually the most of m2p_add/remove_override takes effect only if there is a
> >> kmap_op parameter, but what about the rest of the code there?
> > 
> > It is safe to assume that we only need the m2p_override if
> > !xen_feature(XENFEAT_auto_translated_physmap).
> > I wouldn't make any assumptions on kmap_ops != NULL.
> 
> I think it is -- we only need the m2p override if we have userspace
> mappings (where kmap_ops != 0).
>
> > I would remove the bool m2p_override parameter completely and determine
> > whether we need to call the m2p_override functions from the x86
> > implementation of set/clear_foreign_p2m_mapping by checking
> > xen_feature(XENFEAT_auto_translated_physmap).
> > 
> > David, does it seem reasonable to you?
> 
> That would miss the point of this patch which is to avoid adding to the
> m2p_override for kernel only mappings.

I meant checking 

!xen_feature(XENFEAT_auto_translated_physmap) && kmap_ops != 0

At least this way the "hack" would be entirely self contained in the
arch specific code.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/