Hi Kazu,
On 03/13/2019 01:17 AM, Kazuhito Hagio wrote:
Hi Bhupesh,
-Original Message-
Right now user-space tools like 'makedumpfile' and 'crash' need to rely
on a best-guess method of determining value of 'MAX_PHYSMEM_BITS'
supported by underlying kernel.
This value is used in user-space code to calculate the bit-space
required to store a section for SPARESMEM (similar to the existing
calculation method used in the kernel implementation):
#define SECTIONS_SHIFT(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
Now, regressions have been reported in user-space utilities
like 'makedumpfile' and 'crash' on arm64, with the recently added
kernel support for 52-bit physical address space, as there is
no clear method of determining this value in user-space
(other than reading kernel CONFIG flags).
As per suggestion from makedumpfile maintainer (Kazu), it makes more
sense to append 'MAX_PHYSMEM_BITS' to vmcoreinfo in the core code itself
rather than in arch-specific code, so that the user-space code for other
archs can also benefit from this addition to the vmcoreinfo and use it
as a standard way of determining 'SECTIONS_SHIFT' value in user-land.
A reference 'makedumpfile' implementation which reads the
'MAX_PHYSMEM_BITS' value from vmcoreinfo in a arch-independent fashion
is available here:
[0].
https://github.com/bhupesh-sharma/makedumpfile/blob/remove-max-phys-mem-bit-v1/arch/ppc64.c#L471
Cc: Boris Petkov
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: James Morse
Cc: Will Deacon
Cc: Michael Ellerman
Cc: Paul Mackerras
Cc: Benjamin Herrenschmidt
Cc: Dave Anderson
Cc: Kazuhito Hagio
Cc: x...@kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-ker...@vger.kernel.org
Cc: ke...@lists.infradead.org
Signed-off-by: Bhupesh Sharma
---
kernel/crash_core.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 093c9f917ed0..44b90368e183 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -467,6 +467,7 @@ static int __init crash_save_vmcoreinfo_init(void)
#define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline)
VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
#endif
+ VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
Some architectures define MAX_PHYSMEM_BITS only with CONFIG_SPARSEMEM,
so we need to move this to the #ifdef section that exports some
mem_section things.
Thanks!
Kazu
Sorry for the late response, I wanted to make sure I check almost all
archs to understand if a proposal would work for all.
As per my current understanding, we can protect the export of
'MAX_PHYSMEM_BITS' via a #ifdef section against CONFIG_SPARSEMEM, and it
should work for all archs. Here are some arguments to support the same,
would request maintainers of various archs (in Cc) to correct me if I am
missing something here:
1. SPARSEMEM is dependent upon on (!SELECT_MEMORY_MODEL &&
ARCH_SPARSEMEM_ENABLE) || SPARSEMEM_MANUAL:
config SPARSEMEM
def_bool y
depends on (!SELECT_MEMORY_MODEL && ARCH_SPARSEMEM_ENABLE) ||
SPARSEMEM_MANUAL
2. For a couple of archs, this option is already turned on by default in
their respective defconfigs:
$ grep -nrw "CONFIG_SPARSEMEM_MANUAL" *
arch/ia64/configs/gensparse_defconfig:18:CONFIG_SPARSEMEM_MANUAL=y
arch/powerpc/configs/ppc64e_defconfig:30:CONFIG_SPARSEMEM_MANUAL=y
3. Note that other archs use ARCH_SPARSEMEM_DEFAULT to define if
CONFIG_SPARSEMEM_MANUAL is set by default:
choice
prompt "Memory model"
..
default SPARSEMEM_MANUAL if ARCH_SPARSEMEM_DEFAULT
3a.
$ grep -nrw -A 2 "ARCH_SPARSEMEM_DEFAULT" *
arch/s390/Kconfig:621:config ARCH_SPARSEMEM_DEFAULT
arch/s390/Kconfig-622- def_bool y
--
arch/x86/Kconfig:1623:config ARCH_SPARSEMEM_DEFAULT
arch/x86/Kconfig-1624- def_bool y
arch/x86/Kconfig-1625- depends on X86_64
--
arch/powerpc/Kconfig:614:config ARCH_SPARSEMEM_DEFAULT
arch/powerpc/Kconfig-615- def_bool y
arch/powerpc/Kconfig-616- depends on PPC_BOOK3S_64
--
arch/arm64/Kconfig:850:config ARCH_SPARSEMEM_DEFAULT
arch/arm64/Kconfig-851- def_bool ARCH_SPARSEMEM_ENABLE
--
arch/sh/mm/Kconfig:138:config ARCH_SPARSEMEM_DEFAULT
arch/sh/mm/Kconfig-139- def_bool y
--
arch/sparc/Kconfig:315:config ARCH_SPARSEMEM_DEFAULT
arch/sparc/Kconfig-316- def_bool y if SPARC64
--
arch/arm/Kconfig:1591:config ARCH_SPARSEMEM_DEFAULT
arch/arm/Kconfig-1592- def_bool ARCH_SPARSEMEM_ENABLE
Since most archs (except MIPS) set
CONFIG_ARCH_SPARSEMEM_DEFAULT/CONFIG_ARCH_SPARSEMEM_ENABLE to y in the
default configurations, so even though they don't protect
'MAX_PHYSMEM_BITS' define in CONFIG_SPARSEMEM ifdef sections, we still
would be ok protecting the 'MAX_PHYSMEM_BITS' vmcoreinfo export inside a
CONFIG_SPARSEMEM ifdef section.
Thanks for your inputs, I will include this change in the v3.
Regards,
Bhupesh
