Re: [Xen-devel] [RFC PATCH 2/2] x86/mm: Add mem access rights to NPT

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 6/13/19 6:19 PM, Tamas Lengyel wrote:
> On Wed, Sep 26, 2018 at 10:49 AM George Dunlap <george.dunlap@xxxxxxxxxx> wrote:
> > From: Isaila Alexandru <aisaila@xxxxxxxxxxxxxxx>
> >
> > This patch adds access control for NPT mode.
> >
> > There aren’t enough extra bits to store the access rights in the NPT p2m
> > table, so we add a radix tree to store extra information.
> >
> > For efficiency:
> >   - Only allocate this radix tree when we first store "non-default"
> >     extra information
> >
> >   - Remove entires which match the default extra information rather
> >     than continuing to store them
> >
> >   - For superpages, only store an entry for the first gfn in the
> >     superpage.  Use the order of the p2m entry being read to determine
> >     the proper place to look in the radix table.
> >
> > Modify p2m_type_to_flags() to accept and interpret an access value,
> > parallel to the ept code.
> >
> > Add a set_default_access() method to the p2m-pt and p2m-ept versions
> > of the p2m rather than setting it directly, to deal with different
> > default permitted access values.
> >
> > Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> > Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> The mem_access/monitor bits are fairly trivial:
>
> Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
>
> > ---
> > NB, this is compile-tested only.
> Are you planning to do some actual testing? I would highly recommend
> that we see real test results before this is merged to verify
> functionality.
We did do some testing with xen-access at the time, but limited testing 
with the actual full-blown introspection agent (because not all the 
needed pieces align yet).
Things did appear to work as intended.


Thanks,
Razvan

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