arm64: Fix up /proc/cpuinfo
Commit d7a49086 (arm64: cpuinfo: print info for all CPUs) attempted to clean up /proc/cpuinfo, but due to concerns regarding further changes was reverted in commit 5e39977e (Revert "arm64: cpuinfo: print info for all CPUs"). There are two major issues with the arm64 /proc/cpuinfo format currently: * The "Features" line describes (only) the 64-bit hwcaps, which is problematic for some 32-bit applications which attempt to parse it. As the same names are used for analogous ISA features (e.g. aes) despite these generally being architecturally unrelated, it is not possible to simply append the 64-bit and 32-bit hwcaps in a manner that might not be misleading to some applications. Various potential solutions have appeared in vendor kernels. Typically the format of the Features line varies depending on whether the task is 32-bit. * Information is only printed regarding a single CPU. This does not match the ARM format, and does not provide sufficient information in big.LITTLE systems where CPUs are heterogeneous. The CPU information printed is queried from the current CPU's registers, which is racy w.r.t. cross-cpu migration. This patch attempts to solve these issues. The following changes are made: * When a task with a LINUX32 personality attempts to read /proc/cpuinfo, the "Features" line contains the decoded 32-bit hwcaps, as with the arm port. Otherwise, the decoded 64-bit hwcaps are shown. This aligns with the behaviour of COMPAT_UTS_MACHINE and COMPAT_ELF_PLATFORM. In the absense of compat support, the Features line is empty. The set of hwcaps injected into a task's auxval are unaffected. * Properties are printed per-cpu, as with the ARM port. The per-cpu information is queried from pre-recorded cpu information (as used by the sanity checks). * As with the previous attempt at fixing up /proc/cpuinfo, the hardware field is removed. The only users so far are 32-bit applications tied to particular boards, so no portable applications should be affected, and this should prevent future tying to particular boards. The following differences remain: * No model_name is printed, as this cannot be queried from the hardware and cannot be provided in a stable fashion. Use of the CPU {implementor,variant,part,revision} fields is sufficient to identify a CPU and is portable across arm and arm64. * The following system-wide properties are not provided, as they are not possible to provide generally. Programs relying on these are already tied to particular (32-bit only) boards: - Hardware - Revision - Serial No software has yet been identified for which these remaining differences are problematic. Cc: Greg Hackmann <ghackmann@google.com> Cc: Ian Campbell <ijc@hellion.org.uk> Cc: Serban Constantinescu <serban.constantinescu@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: cross-distro@lists.linaro.org Cc: linux-api@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Acked-by:Catalin Marinas <catalin.marinas@arm.com> Signed-off-by:
Mark Rutland <mark.rutland@arm.com> Signed-off-by:
Will Deacon <will.deacon@arm.com>
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