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SubjectRe: [criu] 1M guard page ruined restore
On Wed, Jun 21, 2017 at 07:15:45PM +0200, Oleg Nesterov wrote:
> On 06/21, Oleg Nesterov wrote:
> >
> > On 06/21, Cyrill Gorcunov wrote:
> > >
> > > On Wed, Jun 21, 2017 at 05:57:30PM +0200, Oleg Nesterov wrote:
> > > > >
> > > > > p = fake_grow_down;
> > > > > *p-- = 'c';
> > > >
> > > > I guess this works? I mean, *p-- = 'c' should not fail...
> > >
> > > It fails.
> >
> > Hmm. Impossible ;) could you add the additional printf's to re-check?
>
> Yes, please...

I meant of course second store, sorry for confusion :)

>
> > > p = fake_grow_down;
> > > *p-- = 'c';
> >
> > once again, I can't believe this STORE can fail...
> >
> > > *p = 'b';
> >
> > Ah. I forgot about another kernel "feature" ;) not related to the recent guard
> > page changes...
>
> On the second thought it is actually connected, and it seems we really need to
> remove this code in do_page_fault... I'll re-check tomorrow, need to run away.
>
> > Could you test the patch below?
> >
> > Oleg.
> >
> >
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 8ad91a0..edc5d68 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1416,7 +1416,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> > * and pusha to work. ("enter $65535, $31" pushes
> > * 32 pointers and then decrements %sp by 65535.)
> > */
> > - if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
> > +if (0) if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
> > bad_area(regs, error_code, address);
> > return;
> > }

It does the trick

[root@fc2 ~]# ~/st2
start_addr 7fce7c3f8000
start_addr 7fce7c529000
test_addr 7fce7c527000
grow_down 7fce7c526000

Cyrill

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