[PATCH v3] x86: Properly disable XSAVE related features [BZ #27605]

["H.J. Lu" <hjl.tools@gmail.com>]

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On Fri, Mar 19, 2021 at 3:22 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Fri, Mar 19, 2021 at 2:42 PM DJ Delorie <dj@redhat.com> wrote:
> >
> > "H.J. Lu" <hjl.tools@gmail.com> writes:
> > > If OSXSAVE is disabled by glibc tunables, disable features which depend
> > > on OSXSAVE.
> >
> > This one seems to ignore -XSAVE, both on an 11th gen (-XSAVE,-XSAVEC ->
> > xsave()) and on 4th (just -XSAVE).  Is this patch supposed to be used
> > with the previous patch, or standalone?
> >
>
> Fixed.  Here is the v2 patch.  OK for master?
>

Here is the v3 patch to disable all XSAVE related features if both
XSAVE and XSAVEC aren't usable.

-- 
H.J.

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From 7ed30c76a7e20f77eb1b65f9b38c905819ad1880 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 19 Mar 2021 06:15:37 -0700
Subject: [PATCH v3] x86: Properly disable XSAVE related features [BZ #27605]

1. Support GLIBC_TUNABLES=glibc.cpu.hwcaps=-XSAVE.
2. Disable all features which depend on XSAVE:
   a. If OSXSAVE is disabled by glibc tunables.  Or
   b. If both XSAVE and XSAVEC aren't usable.
---
 sysdeps/x86/cpu-features.c | 55 ++++++++++++++++++++++++++++++++++++++
 sysdeps/x86/cpu-tunables.c |  1 +
 2 files changed, 56 insertions(+)

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index d7248cbb45..e99e67f34d 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -654,6 +654,61 @@ no_cpuid:
 
 #if HAVE_TUNABLES
   TUNABLE_GET (hwcaps, tunable_val_t *, TUNABLE_CALLBACK (set_hwcaps));
+
+  bool disable_xsave_features = false;
+
+  if (!CPU_FEATURE_USABLE_P (cpu_features, OSXSAVE))
+    {
+      /* These features are usable only if OSXSAVE is usable.  */
+      CPU_FEATURE_UNSET (cpu_features, XSAVE);
+      CPU_FEATURE_UNSET (cpu_features, XSAVEOPT);
+      CPU_FEATURE_UNSET (cpu_features, XSAVEC);
+      CPU_FEATURE_UNSET (cpu_features, XGETBV_ECX_1);
+      CPU_FEATURE_UNSET (cpu_features, XFD);
+
+      disable_xsave_features = true;
+    }
+
+  if (disable_xsave_features
+      || (!CPU_FEATURE_USABLE_P (cpu_features, XSAVE)
+	  && !CPU_FEATURE_USABLE_P (cpu_features, XSAVEC)))
+    {
+      /* Clear xsave_state_size if both XSAVE and XSAVEC aren't usable.  */
+      cpu_features->xsave_state_size = 0;
+
+      CPU_FEATURE_UNSET (cpu_features, AVX);
+      CPU_FEATURE_UNSET (cpu_features, AVX2);
+      CPU_FEATURE_UNSET (cpu_features, AVX_VNNI);
+      CPU_FEATURE_UNSET (cpu_features, FMA);
+      CPU_FEATURE_UNSET (cpu_features, VAES);
+      CPU_FEATURE_UNSET (cpu_features, VPCLMULQDQ);
+      CPU_FEATURE_UNSET (cpu_features, XOP);
+      CPU_FEATURE_UNSET (cpu_features, F16C);
+      CPU_FEATURE_UNSET (cpu_features, AVX512F);
+      CPU_FEATURE_UNSET (cpu_features, AVX512CD);
+      CPU_FEATURE_UNSET (cpu_features, AVX512ER);
+      CPU_FEATURE_UNSET (cpu_features, AVX512PF);
+      CPU_FEATURE_UNSET (cpu_features, AVX512VL);
+      CPU_FEATURE_UNSET (cpu_features, AVX512DQ);
+      CPU_FEATURE_UNSET (cpu_features, AVX512BW);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_4FMAPS);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_4VNNIW);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_BITALG);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_IFMA);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_VBMI);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_VBMI2);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_VNNI);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_VPOPCNTDQ);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_VP2INTERSECT);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_BF16);
+      CPU_FEATURE_UNSET (cpu_features, AVX512_FP16);
+      CPU_FEATURE_UNSET (cpu_features, AMX_BF16);
+      CPU_FEATURE_UNSET (cpu_features, AMX_TILE);
+      CPU_FEATURE_UNSET (cpu_features, AMX_INT8);
+
+      CPU_FEATURE_UNSET (cpu_features, FMA4);
+    }
+
 #elif defined SHARED
   /* Reuse dl_platform, dl_hwcap and dl_hwcap_mask for x86.  The
      glibc.cpu.hwcap_mask tunable is initialized already, so no
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 126896f41b..61b05e5b1d 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -168,6 +168,7 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, MOVBE, 5);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SHSTK, 5);
 	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, SSSE3, 5);
+	      CHECK_GLIBC_IFUNC_CPU_OFF (n, cpu_features, XSAVE, 5);
 	    }
 	  break;
 	case 6:
-- 
2.30.2