[linux-next PATCH] arm64: fix kernel crash with 48-bit VA and 64KB granule
Dennis Chen
dennis.chen at arm.com
Tue Jan 5 23:38:49 PST 2016
On Wed, Jan 06, 2016 at 08:13:24AM +0100, Ard Biesheuvel wrote:
> On 6 January 2016 at 07:14, Dennis Chen <dennis.chen at arm.com> wrote:
> > On Tue, Jan 05, 2016 at 09:56:03AM +0000, Catalin Marinas wrote:
> >> On Tue, Jan 05, 2016 at 04:40:44PM +0800, Dennis Chen wrote:
> >> > On Tue, Jan 05, 2016 at 09:38:11AM +0100, Ard Biesheuvel wrote:
> >> > > >> On 5 January 2016 at 03:18, Dennis Chen <dennis.chen at arm.com> wrote:
> >> > > >> > The commit 3400749b5a22 ("arm64/efi: refactor EFI init and runtime
> >> > > >> > code for reuse by 32-bit ARM") uses pgd_alloc() to allocate space for
> >> > > >> > efi_mm.pgd while not the static efi_pgd[], since this function will be
> >> > > >> > called with early_initcall, which results in the pgd_cache used by
> >> > > >> > pgd_alloc() has not been initialized yet, kernel will hang in this
> >> > > >> > case. This patch is trying to make the pgd_cache_init() called before
> >> > > >> > arm_enable_runtime_services() by changing its core_initcall to
> >> > > >> > early_initcall.
> >> > > >> >
> >> > > >> > Signed-off-by: Dennis Chen <dennis.chen at arm.com>
> >> > > >> > Tested-by: Sudeep Holla <sudeep.holla at arm.com>
> >> > > >> >
> >> > > >> > Cc: Will Deacon <will.deacon at arm.com>
> >> > > >> > Cc: Catalin Marinas <catalin.marinas at arm.com>
> >> > > >> > Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> >> > > >> > Cc: Sudeep Holla <sudeep.holla at arm.com>
> >> > > >> > ---
> >> > > >> > arch/arm64/mm/pgd.c | 2 +-
> >> > > >> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >> > > >> >
> >> > > >> > diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> >> > > >> > index cb3ba1b..859a788 100644
> >> > > >> > --- a/arch/arm64/mm/pgd.c
> >> > > >> > +++ b/arch/arm64/mm/pgd.c
> >> > > >> > @@ -56,4 +56,4 @@ static int __init pgd_cache_init(void)
> >> > > >> > SLAB_PANIC, NULL);
> >> > > >> > return 0;
> >> > > >> > }
> >> > > >> > -core_initcall(pgd_cache_init);
> >> > > >> > +early_initcall(pgd_cache_init);
> >> [...]
> >> > > Well, since arm_enable_runtime_services() is an early_initcall()
> >> > > itself, how are you guaranteeing the ordering between the two? Link
> >> > > order?
> >> >
> >> > Link order.
> >>
> >> And can you explain how this works, what guarantees it gives?
> >>
> > You can take a look at include/asm-generic/vmlinux.ldx.h: INIT_CALLS macro,
> > for the init call section, early_initcall is the first chuck in the section,
> > followed by LEVEL[0-7]. For the same level, the layout order is determined
> > by the link order, ARCH is always precedence over the drivers. Catalin, are
> > you giving me a kernel examination? :)
> >
>
> We all know how initcalls are implemented. The question is how you are
> going to ensure that the early_initcall() that initializes the PGD
> cache is always invoked before the early_initcall() that creates the
> UEFI runtime page tables.
>
> And saying that the currently observed link order happens to be
> correct is not good enough. We need to be sure that, even if we change
> the link order, or switch to LTO at some point, things don't suddenly
> break again.
>
Well, if the build system changes the link order, it can't make sure it will break something
unexpectedly, needless to say the pgd_cache_init here at all. Do you think the kernel
will change its currently link order policy? If the answer is yes, what's the benefit?
> --
> Ard.
>
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