x86/speculation: Fix incorrect MDS/TAA mitigation status

For MDS vulnerable processors with TSX support, enabling either MDS or
TAA mitigations will enable the use of VERW to flush internal processor
buffers at the right code path. IOW, they are either both mitigated
or both not. However, if the command line options are inconsistent,
the vulnerabilites sysfs files may not report the mitigation status
correctly.

For example, with only the "mds=off" option:

  vulnerabilities/mds:Vulnerable; SMT vulnerable
  vulnerabilities/tsx_async_abort:Mitigation: Clear CPU buffers; SMT vulnerable

The mds vulnerabilities file has wrong status in this case. Similarly,
the taa vulnerability file will be wrong with mds mitigation on, but
taa off.

Change taa_select_mitigation() to sync up the two mitigation status
and have them turned off if both "mds=off" and "tsx_async_abort=off"
are present.

Update documentation to emphasize the fact that both "mds=off" and
"tsx_async_abort=off" have to be specified together for processors that
are affected by both TAA and MDS to be effective.

 [ bp: Massage and add kernel-parameters.txt change too. ]

Fixes: 1b42f017415b ("x86/speculation/taa: Add mitigation for TSX Async Abort")
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: [email protected]
Cc: Mark Gross <[email protected]>
Cc: <[email protected]>
Cc: Pawan Gupta <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Tyler Hicks <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions