linux_dsm_epyc7002/arch/arm64/kernel
Will Deacon 2a2830703a arm64: debug: avoid accessing mdscr_el1 on fault paths where possible
Since mdscr_el1 is part of the debug register group, it is highly likely
to be trapped by a hypervisor to prevent virtual machines from debugging
(buggering?) each other. Unfortunately, this absolutely destroys our
performance, since we access the register on many of our low-level
fault handling paths to keep track of the various debug state machines.

This patch removes our dependency on mdscr_el1 in the case that debugging
is not being used. More specifically we:

  - Use TIF_SINGLESTEP to indicate that a task is stepping at EL0 and
    avoid disabling step in the MDSCR when we don't need to.
    MDSCR_EL1.SS handling is moved to kernel_entry, when trapping from
    userspace.

  - Ensure debug exceptions are re-enabled on *all* exception entry
    paths, even the debug exception handling path (where we re-enable
    exceptions after invoking the handler). Since we can now rely on
    MDSCR_EL1.SS being cleared by the entry code, exception handlers can
    usually enable debug immediately before enabling interrupts.

  - Remove all debug exception unmasking from ret_to_user and
    el1_preempt, since we will never get here with debug exceptions
    masked.

This results in a slight change to kernel debug behaviour, where we now
step into interrupt handlers and data aborts from EL1 when debugging the
kernel, which is actually a useful thing to do. A side-effect of this is
that it *does* potentially prevent stepping off {break,watch}points when
there is a high-frequency interrupt source (e.g. a timer), so a debugger
would need to use either breakpoints or manually disable interrupts to
get around this issue.

With this patch applied, guest performance is restored under KVM when
debug register accesses are trapped (and we get a measurable performance
increase on the host on Cortex-A57 too).

Cc: Ian Campbell <ian.campbell@citrix.com>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2014-05-12 16:43:28 +01:00
..
vdso arm64: vdso: fix coarse clock handling 2014-02-05 11:55:30 +00:00
.gitignore arm64: Build infrastructure 2012-09-17 13:42:21 +01:00
arm64ksyms.c arm64: use generic strnlen_user and strncpy_from_user functions 2013-12-19 17:43:06 +00:00
asm-offsets.c arm64: kernel: cpu_{suspend/resume} implementation 2013-12-16 17:17:31 +00:00
cpu_ops.c arm64: Slightly improve the warning on CPU0 enable-method 2013-10-31 16:37:26 +00:00
cputable.c arm64: add CPU_HOTPLUG infrastructure 2013-10-25 11:33:21 +01:00
debug-monitors.c arm64: debug: remove noisy, pointless warning 2014-04-25 16:46:50 +01:00
early_printk.c arm64: fixmap: fix missing sub-page offset for earlyprintk 2014-05-03 22:20:31 +01:00
entry-fpsimd.S arm64: move FP-SIMD save/restore code to a macro 2012-12-05 11:26:50 +00:00
entry.S arm64: debug: avoid accessing mdscr_el1 on fault paths where possible 2014-05-12 16:43:28 +01:00
fpsimd.c arm64: kernel: implement fpsimd CPU PM notifier 2013-12-16 17:17:32 +00:00
head.S arm64: head: fix cache flushing and barriers in set_cpu_boot_mode_flag 2014-05-09 17:04:12 +01:00
hw_breakpoint.c arm64, hw_breakpoint.c: Fix CPU hotplug callback registration 2014-03-20 13:43:44 +01:00
hyp-stub.S arm64: add hypervisor stub 2012-12-05 11:26:49 +00:00
insn.c arm64: introduce aarch64_insn_gen_{nop|branch_imm}() helper functions 2014-01-08 15:21:29 +00:00
io.c arm64: Device specific operations 2012-09-17 13:42:04 +01:00
irq.c arm64: add CPU_HOTPLUG infrastructure 2013-10-25 11:33:21 +01:00
jump_label.c arm64, jump label: optimize jump label implementation 2014-01-08 15:23:53 +00:00
kgdb.c arm64: KGDB: Add step debugging support 2014-02-26 11:16:25 +00:00
kuser32.S arm64: atomics: fix use of acquire + release for full barrier semantics 2014-02-07 16:45:43 +00:00
Makefile ARM64: perf: add support for perf registers API 2014-03-13 11:22:37 +00:00
module.c arm64: move encode_insn_immediate() from module.c to insn.c 2014-01-08 15:21:29 +00:00
perf_event.c arm64: fix !CONFIG_COMPAT build failures 2014-04-06 23:25:04 +01:00
perf_regs.c arm64: fix !CONFIG_COMPAT build failures 2014-04-06 23:25:04 +01:00
process.c arm64: barriers: make use of barrier options with explicit barriers 2014-05-09 17:03:15 +01:00
psci.c arm64: remove return value form psci_init() 2014-02-28 14:14:53 +00:00
ptrace.c arm64: ptrace: avoid using HW_BREAKPOINT_EMPTY for disabled events 2013-12-19 17:41:25 +00:00
setup.c arm64: Clean up the default pgprot setting 2014-05-09 15:53:37 +01:00
signal32.c arm64: Provide read/write fault information in compat signal handlers 2014-05-09 15:47:47 +01:00
signal.c arm64: Expose ESR_EL1 information to user when SIGSEGV/SIGBUS 2014-05-09 15:47:49 +01:00
sleep.S arm64: kernel: cpu_{suspend/resume} implementation 2013-12-16 17:17:31 +00:00
smp_spin_table.c arm64: Remove boot thread synchronisation for spin-table release method 2014-05-09 15:47:46 +01:00
smp.c arm64: topology: Implement basic CPU topology support 2014-03-04 10:30:07 +00:00
stacktrace.c ARM64: unwind: Fix PC calculation 2014-02-17 09:16:33 +00:00
suspend.c arm64: kernel: fix per-cpu offset restore on resume 2014-01-24 14:27:40 +00:00
sys32.S arm64: compat: correct register concatenation for syscall wrappers 2013-10-25 15:59:36 +01:00
sys_compat.c compat: generic compat_sys_sched_rr_get_interval() implementation 2012-12-17 17:15:18 -08:00
sys.c arm64: switch to generic sigaltstack 2013-02-14 09:17:29 -05:00
time.c arm64: init: Move of_clk_init to time_init 2014-04-25 18:15:56 +01:00
topology.c arm64: topology: Implement basic CPU topology support 2014-03-04 10:30:07 +00:00
traps.c arm64: Provide read/write fault information in compat signal handlers 2014-05-09 15:47:47 +01:00
vdso.c arm64: vdso: clean up vdso_pagelist initialization 2014-02-26 11:16:30 +00:00
vmlinux.lds.S arm64: Remove unused __data_loc variable 2013-12-20 12:04:48 +00:00