* [PATCH v2] x86: Set FSGSBASE to active if enabled by kernel
@ 2023-03-16 0:42 H.J. Lu
2023-04-03 12:25 ` Florian Weimer
0 siblings, 1 reply; 2+ messages in thread
From: H.J. Lu @ 2023-03-16 0:42 UTC (permalink / raw)
To: libc-alpha; +Cc: Florian Weimer
Linux kernel uses AT_HWCAP2 to indicate if FSGSBASE instructions are
enabled. If the HWCAP2_FSGSBASE bit in AT_HWCAP2 is set, FSGSBASE
instructions can be used in user space. Define dl_check_hwcap2 to set
the FSGSBASE feature to active on Linux when the HWCAP2_FSGSBASE bit is
set.
Add a test to verify that FSGSBASE is active on current kernels.
NB: This test will fail if the kernel doesn't set the HWCAP2_FSGSBASE
bit in AT_HWCAP2 while fsgsbase shows up in /proc/cpuinfo.
---
sysdeps/unix/sysv/linux/x86/dl-hwcap2.h | 27 +++++++++++++++++++++++++
sysdeps/x86/cpu-features.c | 3 +++
sysdeps/x86/dl-hwcap2.h | 21 +++++++++++++++++++
sysdeps/x86/tst-cpu-features-cpuinfo.c | 7 +++++++
4 files changed, 58 insertions(+)
create mode 100644 sysdeps/unix/sysv/linux/x86/dl-hwcap2.h
create mode 100644 sysdeps/x86/dl-hwcap2.h
diff --git a/sysdeps/unix/sysv/linux/x86/dl-hwcap2.h b/sysdeps/unix/sysv/linux/x86/dl-hwcap2.h
new file mode 100644
index 0000000000..28f38ea510
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/dl-hwcap2.h
@@ -0,0 +1,27 @@
+/* Handle AT_HWCAP2. Linux/x86 version.
+ Copyright (C) 2023 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* The following must match the kernel's <asm/hwcap2.h>. */
+#define HWCAP2_RING3MWAIT (1 << 0)
+#define HWCAP2_FSGSBASE (1 << 1)
+
+static inline void
+dl_check_hwcap2 (struct cpu_features *cpu_features)
+{
+ if ((GLRO(dl_hwcap2) & HWCAP2_FSGSBASE) != 0)
+ CPU_FEATURE_SET_ACTIVE (cpu_features, FSGSBASE);
+}
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 822688e21f..05f966ea64 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -22,6 +22,7 @@
#include <cacheinfo.h>
#include <dl-cacheinfo.h>
#include <dl-minsigstacksize.h>
+#include <dl-hwcap2.h>
#if HAVE_TUNABLES
extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *)
@@ -303,6 +304,8 @@ update_active (struct cpu_features *cpu_features)
CPU_FEATURE_SET_ACTIVE (cpu_features, WIDE_KL);
}
+ dl_check_hwcap2 (cpu_features);
+
cpu_features->isa_1 = get_isa_level (cpu_features);
}
diff --git a/sysdeps/x86/dl-hwcap2.h b/sysdeps/x86/dl-hwcap2.h
new file mode 100644
index 0000000000..73cd6cc37d
--- /dev/null
+++ b/sysdeps/x86/dl-hwcap2.h
@@ -0,0 +1,21 @@
+/* Handle AT_HWCAP2. Generic x86 version.
+ Copyright (C) 2023 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+static inline void
+dl_check_hwcap2 (struct cpu_features *cpu_features)
+{
+}
diff --git a/sysdeps/x86/tst-cpu-features-cpuinfo.c b/sysdeps/x86/tst-cpu-features-cpuinfo.c
index c25240774e..544171028d 100644
--- a/sysdeps/x86/tst-cpu-features-cpuinfo.c
+++ b/sysdeps/x86/tst-cpu-features-cpuinfo.c
@@ -96,6 +96,11 @@ check_proc (const char *proc_name, const char *search_name, int flag,
CPU_FEATURE_USABLE (name), \
"HAS_CPU_FEATURE (" #name ")")
+#define CHECK_PROC_ACTIVE(str, name) \
+ check_proc (#str, " "#str" ", CPU_FEATURE_USABLE (name), \
+ CPU_FEATURE_USABLE (name), \
+ "CPU_FEATURE_USABLE (" #name ")")
+
static int
do_test (int argc, char **argv)
{
@@ -295,6 +300,8 @@ do_test (int argc, char **argv)
fails += CHECK_PROC (xsaves, XSAVES);
fails += CHECK_PROC (xtpr, XTPRUPDCTRL);
+ fails += CHECK_PROC_ACTIVE (fsgsbase, FSGSBASE);
+
printf ("%d differences between /proc/cpuinfo and glibc code.\n", fails);
return (fails != 0);
--
2.39.2
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v2] x86: Set FSGSBASE to active if enabled by kernel
2023-03-16 0:42 [PATCH v2] x86: Set FSGSBASE to active if enabled by kernel H.J. Lu
@ 2023-04-03 12:25 ` Florian Weimer
0 siblings, 0 replies; 2+ messages in thread
From: Florian Weimer @ 2023-04-03 12:25 UTC (permalink / raw)
To: H.J. Lu; +Cc: libc-alpha
* H. J. Lu:
> Linux kernel uses AT_HWCAP2 to indicate if FSGSBASE instructions are
> enabled. If the HWCAP2_FSGSBASE bit in AT_HWCAP2 is set, FSGSBASE
> instructions can be used in user space. Define dl_check_hwcap2 to set
> the FSGSBASE feature to active on Linux when the HWCAP2_FSGSBASE bit is
> set.
>
> Add a test to verify that FSGSBASE is active on current kernels.
> NB: This test will fail if the kernel doesn't set the HWCAP2_FSGSBASE
> bit in AT_HWCAP2 while fsgsbase shows up in /proc/cpuinfo.
This version looks good to me.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Thanks,
Florian
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-04-03 12:25 ` Florian Weimer
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