]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR
authorXiaoyao Li <xiaoyao.li@intel.com>
Wed, 25 Mar 2020 03:09:24 +0000 (11:09 +0800)
committerThomas Gleixner <tglx@linutronix.de>
Fri, 27 Mar 2020 10:43:30 +0000 (11:43 +0100)
commita6a60741035bb48ca8d9f92a138958818148064c
treec4ad4d6fc86dd4ef0e3fc15b753db88742bc60bb
parentdbaba47085b0c2aa793ce849750164bd3765e163
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
arch/x86/kernel/cpu/intel.c