Subject: Re: [next] arm64: boot failed - next-20220606

From: Catalin Marinas <[email-masked]>
Date: Thu, 9 Jun 2022 11:25:55 +0100

On Thu, Jun 09, 2022 at 11:11:54AM +0100, Will Deacon wrote:
> On Thu, Jun 09, 2022 at 11:44:09AM +0800, Kefeng Wang wrote:
> > On 2022/6/9 10:49, Vasily Averin wrote:
> > > mem_cgroup_from_obj():
> > > ffff80000836cf40:       d503245f        bti     c
> > > ffff80000836cf44:       d503201f        nop
> > > ffff80000836cf48:       d503201f        nop
> > > ffff80000836cf4c:       d503233f        paciasp
> > > ffff80000836cf50:       d503201f        nop
> > > ffff80000836cf54:       d2e00021        mov     x1, #0x1000000000000            // #281474976710656
> > > ffff80000836cf58:       8b010001        add     x1, x0, x1
> > > ffff80000836cf5c:       b25657e4        mov     x4, #0xfffffc0000000000         // #-4398046511104
> > > ffff80000836cf60:       d34cfc21        lsr     x1, x1, #12
> > > ffff80000836cf64:       d37ae421        lsl     x1, x1, #6
> > > ffff80000836cf68:       8b040022        add     x2, x1, x4
> > > ffff80000836cf6c:       f9400443        ldr     x3, [x2, #8]
> > > 
> > > x5 : ffff80000a96f000 x4 : fffffc0000000000 x3 : ffff80000ad5e680
> > > x2 : fffffe00002bc240 x1 : 00000200002bc240 x0 : ffff80000af09740
> > > 
> > > x0 = 0xffff80000af09740 is an argument of mem_cgroup_from_obj()
> > > according to System.map it is init_net
> > > 
> > > This issue is caused by calling virt_to_page() on address of static variable init_net.
> > > Arm64 consider that addresses of static variables are not valid virtual addresses.
> > > On x86_64 the same API works without any problem.
> 
> This just depends on whether or not the kernel is running out of the linear
> mapping or not. On arm64, we use the vmalloc area for the kernel image and
> so virt_to_page() won't work, just like it won't work for modules on other
> architectures.
> 
> How are module addresses handled by mem_cgroup_from_obj()?

It doesn't look like they are handled in any way. It just expects the
pointer to be a linear map one. Something like below:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 27cebaa53472..795bf3673fa7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2860,6 +2860,11 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
 	if (mem_cgroup_disabled())
 		return NULL;
 
+	if (is_module_address((unsigned long)p))
+		return NULL;
+	else if (is_kernel((unsigned long)p))
+		return NULL;
+
 	folio = virt_to_folio(p);
 
 	/*

-- 
Catalin