diff options
| author | Xiaoyao Li | 2020-03-25 11:09:24 +0800 |
|---|---|---|
| committer | Thomas Gleixner | 2020-03-27 11:43:30 +0100 |
| commit | a6a60741035bb48ca8d9f92a138958818148064c (patch) | |
| tree | c4ad4d6fc86dd4ef0e3fc15b753db88742bc60bb /arch/x86/kernel/cpu | |
| parent | dbaba47085b0c2aa793ce849750164bd3765e163 (diff) | |
x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR
In a context switch from a task that is detecting split locks to one that
is not (or vice versa) we need to update the TEST_CTRL MSR. Currently this
is done with the common sequence:
read the MSR
flip the bit
write the MSR
in order to avoid changing the value of any reserved bits in the MSR.
Cache unused and reserved bits of TEST_CTRL MSR with SPLIT_LOCK_DETECT bit
cleared during initialization, so we can avoid an expensive RDMSR
instruction during context switch.
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Originally-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200325030924.132881-3-xiaoyao.li@intel.com
Diffstat (limited to 'arch/x86/kernel/cpu')
| -rw-r--r-- | arch/x86/kernel/cpu/intel.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 0c859c91d008..9a26e972cdea 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -45,6 +45,7 @@ enum split_lock_detect_state { * split lock detect, unless there is a command line override. */ static enum split_lock_detect_state sld_state __ro_after_init = sld_off; +static u64 msr_test_ctrl_cache __ro_after_init; /* * Processors which have self-snooping capability can handle conflicting @@ -1034,6 +1035,8 @@ static void __init split_lock_setup(void) break; } + rdmsrl(MSR_TEST_CTRL, msr_test_ctrl_cache); + if (!split_lock_verify_msr(true)) { pr_info("MSR access failed: Disabled\n"); return; @@ -1050,14 +1053,10 @@ static void __init split_lock_setup(void) */ static void sld_update_msr(bool on) { - u64 test_ctrl_val; - - rdmsrl(MSR_TEST_CTRL, test_ctrl_val); + u64 test_ctrl_val = msr_test_ctrl_cache; if (on) test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT; - else - test_ctrl_val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT; wrmsrl(MSR_TEST_CTRL, test_ctrl_val); } |