Re: [Xen-devel] [PATCH v5 1/3] x86/mm: Change default value for suppress #VE in set_mem_access()

[Adrian Pop <apop@xxxxxxxxxxxxxxx>]

On Tue, Sep 11, 2018 at 12:08:42PM -0600, Tamas K Lengyel wrote:
> On Mon, Sep 3, 2018 at 9:48 AM Adrian Pop <apop@xxxxxxxxxxxxxxx> wrote:
> >
> > From: Vlad Ioan Topan <itopan@xxxxxxxxxxxxxxx>
> >
> > The default value for the "suppress #VE" bit set by set_mem_access()
> > currently depends on whether the call is made from the same domain (the
> > bit is set when called from another domain and cleared if called from
> > the same domain). This patch changes that behavior to inherit the old
> > suppress #VE bit value if it is already set and to set it to 1
> > otherwise, which is safer and more reliable.
> >
> > Signed-off-by: Vlad Ioan Topan <itopan@xxxxxxxxxxxxxxx>
> > Signed-off-by: Adrian Pop <apop@xxxxxxxxxxxxxxx>
> > ---
> >  xen/arch/x86/mm/mem_access.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> > index 84d260ebd8..e1522a0b75 100644
> > --- a/xen/arch/x86/mm/mem_access.c
> > +++ b/xen/arch/x86/mm/mem_access.c
> > @@ -284,8 +284,7 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct 
> > p2m_domain *hp2m,
> >          }
> >      }
> >
> > -    return ap2m->set_entry(ap2m, gfn, mfn, PAGE_ORDER_4K, t, a,
> > -                           current->domain != d);
> 
> Could you add a comment here saying "inherit the old suppress #VE bit
> value if it is already set and to set it to 1 otherwise" to explain
> the meaning of the magic -1 value?

Sure.  Thank you!

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