linux-imx

LF-419 arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo

vabits_actual variable on arm64 indicates the actual VA space size,
and allows a single binary to support both 48-bit and 52-bit VA
spaces.

If the ARMv8.2-LVA optional feature is present, and we are running
with a 64KB page size; then it is possible to use 52-bits of address
space for both userspace and kernel addresses. However, any kernel
binary that supports 52-bit must also be able to fall back to 48-bit
at early boot time if the hardware feature is not present.

Since TCR_EL1.T1SZ indicates the size offset of the memory region
addressed by TTBR1_EL1 (and hence can be used for determining the
vabits_actual value) it makes more sense to export the same in
vmcoreinfo rather than vabits_actual variable, as the name of the
variable can change in future kernel versions, but the architectural
constructs like TCR_EL1.T1SZ can be used better to indicate intended
specific fields to user-space.

User-space utilities like makedumpfile and crash-utility, need to
read/write this value from/to vmcoreinfo for determining if a virtual
address lies in the linear map range.

The user-space computation for determining whether an address lies in
the linear map range is the same as we have in kernel-space:

  #define __is_lm_address(addr)	(!(((u64)addr) & BIT(vabits_actual - 1)))

I have sent out user-space patches for makedumpfile and crash-utility
to add features for obtaining vabits_actual value from TCR_EL1.T1SZ (see
[0] and [1]).

Akashi reported that he was able to use this patchset and the user-space
changes to get user-space working fine with the 52-bit kernel VA
changes (see [2]).

[0]. http://lists.infradead.org/pipermail/kexec/2019-November/023966.html
[1]. http://lists.infradead.org/pipermail/kexec/2019-November/024006.html
[2]. http://lists.infradead.org/pipermail/kexec/2019-November/023992.html

Cc: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Steve Capper <steve.capper@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
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>
Tested-by: Poonam Aggrwal <poonam.aggrwal@nxp.com>
Acked-by: Li Yang <leoyang.li@nxp.com>