[PATCH v3 0/3] Append new variables to vmcoreinfo (PTRS_PER_PGD for arm64 and MAX_PHYSMEM_BITS for all archs)

[PATCH v3 0/3] Append new variables to vmcoreinfo (PTRS_PER_PGD for arm64 and MAX_PHYSMEM_BITS for all archs)

[Bhupesh Sharma]

Changes since v2:
----------------
- v2 can be seen here:
  http://lists.infradead.org/pipermail/kexec/2019-March/022531.html
- Protected 'MAX_PHYSMEM_BITS' vmcoreinfo variable under CONFIG_SPARSEMEM
  ifdef sections, as suggested by Kazu.
- Updated vmcoreinfo documentation to add description about
  'MAX_PHYSMEM_BITS' variable (via [PATCH 3/3]).

Changes since v1:
----------------
- v1 was sent out as a single patch which can be seen here:
  http://lists.infradead.org/pipermail/kexec/2019-February/022411.html

- v2 breaks the single patch into two independent patches:
  [PATCH 1/2] appends 'PTRS_PER_PGD' to vmcoreinfo for arm64 arch, whereas
  [PATCH 2/2] appends 'MAX_PHYSMEM_BITS' to vmcoreinfo in core kernel code (all archs)

This patchset primarily fixes the regression reported in user-space
utilities like 'makedumpfile' and 'crash-utility' on arm64 architecture
with the availability of 52-bit address space feature in underlying
kernel. These regressions have been reported both on CPUs which don't
support ARMv8.2 extensions (i.e. LVA, LPA) and are running newer kernels
and also on prototype platforms (like ARMv8 FVP simulator model) which
support ARMv8.2 extensions and are running newer kernels.

The reason for these regressions is that right now user-space tools
have no direct access to these values (since these are not exported
from the kernel) and hence need to rely on a best-guess method of
determining value of 'PTRS_PER_PGD' and 'MAX_PHYSMEM_BITS' supported
by underlying kernel.

Exporting these values via vmcoreinfo will help user-land in such cases.
In addition, 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 arm64 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.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Boris Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: x86@kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org

Bhupesh Sharma (3):
  arm64, vmcoreinfo : Append 'PTRS_PER_PGD' to vmcoreinfo
  crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo
  Documentation/vmcoreinfo: Add documentation for 'MAX_PHYSMEM_BITS'

 Documentation/kdump/vmcoreinfo.txt | 5 +++++
 arch/arm64/kernel/crash_core.c     | 1 +
 kernel/crash_core.c                | 1 +
 3 files changed, 7 insertions(+)

-- 
2.7.4

[PATCH v3 2/3] crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo

[Bhupesh Sharma]

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 <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: x86@kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
---
 kernel/crash_core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 093c9f917ed0..495f09084696 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -415,6 +415,7 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
 	VMCOREINFO_STRUCT_SIZE(mem_section);
 	VMCOREINFO_OFFSET(mem_section, section_mem_map);
+	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
 #endif
 	VMCOREINFO_STRUCT_SIZE(page);
 	VMCOREINFO_STRUCT_SIZE(pglist_data);
-- 
2.7.4

[PATCH v3 3/3] Documentation/vmcoreinfo: Add documentation for 'MAX_PHYSMEM_BITS'

[Bhupesh Sharma]

Add documentation for 'MAX_PHYSMEM_BITS' variable being added to
vmcoreinfo.

'MAX_PHYSMEM_BITS' defines the maximum supported physical address
space memory.

Cc: Boris Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: x86@kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
---
 Documentation/kdump/vmcoreinfo.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Documentation/kdump/vmcoreinfo.txt b/Documentation/kdump/vmcoreinfo.txt
index bb94a4bd597a..f5a11388dc49 100644
--- a/Documentation/kdump/vmcoreinfo.txt
+++ b/Documentation/kdump/vmcoreinfo.txt
@@ -95,6 +95,11 @@ It exists in the sparse memory mapping model, and it is also somewhat
 similar to the mem_map variable, both of them are used to translate an
 address.
 
+MAX_PHYSMEM_BITS
+----------------
+
+Defines the maximum supported physical address space memory.
+
 page
 ----
 
-- 
2.7.4