Re: [PATCH 1/3] mm: Make generic arch_is_kernel_initmem_freed() do what it says
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2021-09-27 13:12:10
Also in:
linux-arch, linux-mm, linux-s390, lkml
Christophe Leroy [off-list ref] writes:
quoted hunk ↗ jump to hunk
Commit 7a5da02de8d6 ("locking/lockdep: check for freed initmem in static_obj()") added arch_is_kernel_initmem_freed() which is supposed to report whether an object is part of already freed init memory. For the time being, the generic version of arch_is_kernel_initmem_freed() always reports 'false', allthough free_initmem() is generically called on all architectures. Therefore, change the generic version of arch_is_kernel_initmem_freed() to check whether free_initmem() has been called. If so, then check if a given address falls into init memory. In order to use function init_section_contains(), the fonction is moved at the end of asm-generic/section.h Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Signed-off-by: Christophe Leroy <redacted> --- include/asm-generic/sections.h | 31 +++++++++++++++++-------------- 1 file changed, 17 insertions(+), 14 deletions(-)diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h index d16302d3eb59..d1e5bb2c6b72 100644 --- a/include/asm-generic/sections.h +++ b/include/asm-generic/sections.h@@ -172,4 +158,21 @@ static inline bool is_kernel_rodata(unsigned long addr) addr < (unsigned long)__end_rodata; } +/* + * Check if an address is part of freed initmem. This is needed on architectures + * with virt == phys kernel mapping, for code that wants to check if an address + * is part of a static object within [_stext, _end]. After initmem is freed, + * memory can be allocated from it, and such allocations would then have + * addresses within the range [_stext, _end]. + */ +#ifndef arch_is_kernel_initmem_freed +static inline int arch_is_kernel_initmem_freed(unsigned long addr) +{ + if (system_state < SYSTEM_RUNNING) + return 0; + + return init_section_contains((void *)addr, 1); +} +#endif
This will return an incorrect result for a short period during boot
won't it?
See init/main.c:
static int __ref kernel_init(void *unused)
{
...
free_initmem(); <- memory is freed here
mark_readonly();
/*
* Kernel mappings are now finalized - update the userspace page-table
* to finalize PTI.
*/
pti_finalize();
system_state = SYSTEM_RUNNING;
After free_initmem() we have address ranges that are now freed initmem,
but arch_is_kernel_initmem_freed() continues to return 0 (false) for all
addresses, until we update system_state.
Possibly that doesn't matter for any of the current callers, but it
seems pretty dicey to me.
cheers