Re: [PATCH] xen/arm: alternative: Don't call vmap() within stop_machine_run()

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 27/04/2022 07:42, Jan Beulich wrote:
> On 26.04.2022 22:06, Julien Grall wrote:
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > Commit 88a037e2cfe1 "page_alloc: assert IRQs are enabled in heap
> > alloc/free" extended the checks in the buddy allocator to catch
> > any use of the helpers from context with interrupts disabled.
> >
> > Unfortunately, the rule is not followed in the alternative code and
> > this will result to crash at boot with debug enabled:
> >
> > (XEN) Xen call trace:
> > (XEN)    [<0022a510>] alloc_xenheap_pages+0x120/0x150 (PC)
> > (XEN)    [<00000000>] 00000000 (LR)
> > (XEN)    [<002736ac>] arch/arm/mm.c#xen_pt_update+0x144/0x6e4
> > (XEN)    [<002740d4>] map_pages_to_xen+0x10/0x20
> > (XEN)    [<00236864>] __vmap+0x400/0x4a4
> > (XEN)    [<0026aee8>] 
> > arch/arm/alternative.c#__apply_alternatives_multi_stop+0x144/0x1ec
> > (XEN)    [<0022fe40>] stop_machine_run+0x23c/0x300
> > (XEN)    [<002c40c4>] apply_alternatives_all+0x34/0x5c
> > (XEN)    [<002ce3e8>] start_xen+0xcb8/0x1024
> > (XEN)    [<00200068>] arch/arm/arm32/head.o#primary_switched+0xc/0x1c
> >
> > The interrupts will be disabled by the state machine in stop_machine_run(),
> > hence why the ASSERT is hit.
> >
> > For now the patch extending the checks has been reverted, but it would
> > be good to re-introduce it (allocation with interrupts disabled is not
> > desirable).
> We definitely should re-apply that patch once the one here went in.
I have commit this patch and also re-apply David's patch.

Cheers,

--
Julien Grall