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x86/tsx: Add config options to set tsx=on|off|auto 

There is a general consensus that TSX usage is not largely spread while
the history shows there is a non trivial space for side channel attacks
possible. Therefore the tsx is disabled by default even on platforms
that might have a safe implementation of TSX according to the current
knowledge. This is a fair trade off to make.

There are, however, workloads that really do benefit from using TSX and
updating to a newer kernel with TSX disabled might introduce a
noticeable regressions. This would be especially a problem for Linux
distributions which will provide TAA mitigations.

Introduce config options X86_INTEL_TSX_MODE_OFF, X86_INTEL_TSX_MODE_ON
and X86_INTEL_TSX_MODE_AUTO to control the TSX feature. The config
setting can be overridden by the tsx cmdline options.

 [ bp: Text cleanups from Josh. ]

Suggested-by: Borislav Petkov <bpetkov@suse.de>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
This commit is contained in:
Michal Hocko 2019-10-23 12:35:50 +02:00 committed by Thomas Gleixner
parent a7a248c593
commit db616173d7
2 changed files with 61 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
arch/x86/Kconfig
View File

@ -1940,6 +1940,51 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS
If unsure, say y.
choice
prompt "TSX enable mode"
depends on CPU_SUP_INTEL
default X86_INTEL_TSX_MODE_OFF
help
Intel's TSX (Transactional Synchronization Extensions) feature
allows to optimize locking protocols through lock elision which
can lead to a noticeable performance boost.
On the other hand it has been shown that TSX can be exploited
to form side channel attacks (e.g. TAA) and chances are there
will be more of those attacks discovered in the future.
Therefore TSX is not enabled by default (aka tsx=off). An admin
might override this decision by tsx=on the command line parameter.
Even with TSX enabled, the kernel will attempt to enable the best
possible TAA mitigation setting depending on the microcode available
for the particular machine.
This option allows to set the default tsx mode between tsx=on, =off
and =auto. See Documentation/admin-guide/kernel-parameters.txt for more
details.
Say off if not sure, auto if TSX is in use but it should be used on safe
platforms or on if TSX is in use and the security aspect of tsx is not
relevant.
config X86_INTEL_TSX_MODE_OFF
bool "off"
help
TSX is disabled if possible - equals to tsx=off command line parameter.
config X86_INTEL_TSX_MODE_ON
bool "on"
help
TSX is always enabled on TSX capable HW - equals the tsx=on command
line parameter.
config X86_INTEL_TSX_MODE_AUTO
bool "auto"
help
TSX is enabled on TSX capable HW that is believed to be safe against
side channel attacks- equals the tsx=auto command line parameter.
endchoice
config EFI
bool "EFI runtime service support"
depends on ACPI

22
arch/x86/kernel/cpu/tsx.c
View File

@ -73,6 +73,14 @@ static bool __init tsx_ctrl_is_supported(void)
return !!(ia32_cap & ARCH_CAP_TSX_CTRL_MSR);
}
static enum tsx_ctrl_states x86_get_tsx_auto_mode(void)
{
if (boot_cpu_has_bug(X86_BUG_TAA))
return TSX_CTRL_DISABLE;
return TSX_CTRL_ENABLE;
}
void __init tsx_init(void)
{
char arg[5] = {};
@ -88,17 +96,19 @@ void __init tsx_init(void)
} else if (!strcmp(arg, "off")) {
tsx_ctrl_state = TSX_CTRL_DISABLE;
} else if (!strcmp(arg, "auto")) {
if (boot_cpu_has_bug(X86_BUG_TAA))
tsx_ctrl_state = TSX_CTRL_DISABLE;
else
tsx_ctrl_state = TSX_CTRL_ENABLE;
tsx_ctrl_state = x86_get_tsx_auto_mode();
} else {
tsx_ctrl_state = TSX_CTRL_DISABLE;
pr_err("tsx: invalid option, defaulting to off\n");
}
} else {
/* tsx= not provided, defaulting to off */
tsx_ctrl_state = TSX_CTRL_DISABLE;
/* tsx= not provided */
if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
tsx_ctrl_state = x86_get_tsx_auto_mode();
else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
tsx_ctrl_state = TSX_CTRL_DISABLE;
else
tsx_ctrl_state = TSX_CTRL_ENABLE;
}
if (tsx_ctrl_state == TSX_CTRL_DISABLE) {