x86: Check RTM_ALWAYS_ABORT for RTM [BZ #28033]

From

https://www.intel.com/content/www/us/en/support/articles/000059422/processors.html

* Intel TSX will be disabled by default.
* The processor will force abort all Restricted Transactional Memory (RTM)
  transactions by default.
* A new CPUID bit CPUID.07H.0H.EDX[11](RTM_ALWAYS_ABORT) will be enumerated,
  which is set to indicate to updated software that the loaded microcode is
  forcing RTM abort.
* On processors that enumerate support for RTM, the CPUID enumeration bits
  for Intel TSX (CPUID.07H.0H.EBX[11] and CPUID.07H.0H.EBX[4]) continue to
  be set by default after microcode update.
* Workloads that were benefited from Intel TSX might experience a change
  in performance.
* System software may use a new bit in Model-Specific Register (MSR) 0x10F
  TSX_FORCE_ABORT[TSX_CPUID_CLEAR] functionality to clear the Hardware Lock
  Elision (HLE) and RTM bits to indicate to software that Intel TSX is
  disabled.

1. Add RTM_ALWAYS_ABORT to CPUID features.
2. Set RTM usable only if RTM_ALWAYS_ABORT isn't set.  This skips the
string/tst-memchr-rtm etc. testcases on the affected processors, which
always fail after a microcde update.
3. Check RTM feature, instead of usability, against /proc/cpuinfo.

This fixes BZ #28033.

(cherry picked from commit ea8e465a6b8d0f26c72bcbe453a854de3abf68ec)

1 files changed, 3 insertions, 0 deletions

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index ffd1bdb10c..b996b8593f 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -333,6 +333,9 @@ init_cpu_features (struct cpu_features *cpu_features)
 
       get_extended_indices (cpu_features);
 
+      if (CPU_FEATURES_CPU_P (cpu_features, RTM_ALWAYS_ABORT))
+	cpu_features->cpuid[index_cpu_RTM].reg_RTM &= ~bit_cpu_RTM;
+
       if (family == 0x06)
 	{
 	  model += extended_model;