Re: [PATCH 1/2] kfence: allow providing __kfence_pool in arch specific way

[Jisheng Zhang <Jisheng.Zhang@synaptics.com>]

On Mon, 24 May 2021 12:36:34 +0200
Marco Elver <elver@google.com> wrote:

> 
> 
> On Mon, 24 May 2021 at 11:26, Jisheng Zhang <Jisheng.Zhang@synaptics.com> wrote:
> > Some architectures may want to allocate the __kfence_pool differently
> > for example, allocate the __kfence_pool earlier before paging_init().
> > We also delay the memset() to kfence_init_pool().
> >
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> > ---
> >  mm/kfence/core.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> > index e18fbbd5d9b4..65f0210edb65 100644
> > --- a/mm/kfence/core.c
> > +++ b/mm/kfence/core.c
> > @@ -430,6 +430,8 @@ static bool __init kfence_init_pool(void)
> >         if (!__kfence_pool)
> >                 return false;
> >
> > +       memset(__kfence_pool, 0, KFENCE_POOL_SIZE);
> > +  
> 
> Use memzero_explicit().
> 
> Also, for the arm64 case, is delaying the zeroing relevant? You still
> call kfence_alloc_pool() in patch 2/2, and zeroing it on
> memblock_alloc() is not wrong, correct?

memblock_alloc() returns virtual address which can't be used before paging_init()
so I delayed the memset to kfence_init_pool.

> 
> Essentially if there's not going to be any benefit to us doing the
> zeroing ourselves, I'd simply leave it as-is and keep using
> memblock_alloc(). And if there's some odd architecture that doesn't
> even want to use kfence_alloc_pool(), they could just zero the memory
> themselves. But we really should use kfence_alloc_pool(), because
> otherwise it'll just become unmaintainable if on changes to
> kfence_alloc_pool() we have to go and find other special architectures
> that don't use it and adjust them, too.
> 
> Thanks,
> -- Marco
> 
> >         if (!arch_kfence_init_pool())
> >                 goto err;
> >
> > @@ -645,10 +647,10 @@ static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
> >
> >  void __init kfence_alloc_pool(void)
> >  {
> > -       if (!kfence_sample_interval)
> > +       if (!kfence_sample_interval || __kfence_pool)
> >                 return;
> >
> > -       __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
> > +       __kfence_pool = memblock_alloc_raw(KFENCE_POOL_SIZE, PAGE_SIZE);
> >
> >         if (!__kfence_pool)
> >                 pr_err("failed to allocate pool\n");
> > --
> > 2.31.0
> >