x86/bugs: Reset speculation control settings on init

stable inclusion
from stable-v4.19.276
commit ca582161f5900991e26240e17f30740a8f3b9f2b
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6TIG1


CVE: NA

--------------------------------

[ Upstream commit 0125acda ]

Currently, x86_spec_ctrl_base is read at boot time and speculative bits
are set if Kconfig items are enabled. For example, IBRS is enabled if
CONFIG_CPU_IBRS_ENTRY is configured, etc. These MSR bits are not cleared
if the mitigations are disabled.

This is a problem when kexec-ing a kernel that has the mitigation
disabled from a kernel that has the mitigation enabled. In this case,
the MSR bits are not cleared during the new kernel boot. As a result,
this might have some performance degradation that is hard to pinpoint.

This problem does not happen if the machine is (hard) rebooted because
the bit will be cleared by default.

  [ bp: Massage. ]

Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20221128153148.1129350-1-leitao@debian.org


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>