[0/2] arm64: Expose physical and virtual address capabilities to user-space

Message

Bhupesh Sharma Jan. 28, 2019, 8:57 p.m. UTC

With ARMv8.2-LVA and LPA architecture extensions, arm64 hardware which
supports these extensions can support upto 52-bit virtual and 52-bit
physical addresses respectively.

Since at the moment we enable the support of these extensions via CONFIG
flags, e.g.
 - LPA via CONFIG_ARM64_PA_BITS_52
   
there are no clear mechanisms in user-space right now to
deteremine these CONFIG flag values and also determine the PARange and
VARange address values.

This patchset proposes two mechanisms to provide a user/user-space
application more information on the same:

1. For a non-expert user, getting an idea about the virtual/physical
   address capabilities on an arm64 hardware via executing:
   $ cat /proc/cpuinfo

   can be quite useful as it provides a similar mechanism as available
   already on x86_64.

   PATCH 1/2 implements the same.

2. For a more involved user/user-space application, the Appendix I:
   Example in 'Documentation/arm64/cpu-feature-registers.txt' is pretty
   useful.

   If we can expose the PARange and VARange values via the MRS register
   reads to user-space, we can use them in user-space programs as a
   standard ABI.

   I already have a 'makedumpfile' user-space example that uses the same
   to determine ARMv8.2-LPA support. See [0].
   
   PATCH 2/2 implements the same.

[0]. https://github.com/bhupesh-sharma/makedumpfile/blob/9d7da4aad3efe79b448f48cc3454fcae46a316d6/arch/arm64.c#L499

Bhupesh Sharma (2):
  arm64: Expose address bits (physical/virtual) via cpuinfo
  arm64: Expose PARange via ID_AA64MMFR0_EL1 and VARange via
    ID_AA64MMFR2_EL1

 arch/arm64/include/asm/cpufeature.h | 59 ++++++++++++++++++++++++-------------
 arch/arm64/include/asm/sysreg.h     | 19 ++++++++++++
 arch/arm64/kernel/cpufeature.c      |  4 +--
 arch/arm64/kernel/cpuinfo.c         |  4 ++-
 4 files changed, 63 insertions(+), 23 deletions(-)