Ensure that a core serializing instruction is issued before returning to
user-mode. x86 implements return to user-space through sysexit, sysrel,
and sysretq, which are not core serializing.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
CC: Thomas Gleixner <t...@linutronix.de>
CC: Andy Lutomirski <l...@kernel.org>
CC: Paul E. McKenney <paul...@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.f...@gmail.com>
CC: Andrew Hunter <a...@google.com>
CC: Maged Michael <maged.mich...@gmail.com>
CC: Avi Kivity <a...@scylladb.com>
CC: Benjamin Herrenschmidt <b...@kernel.crashing.org>
CC: Paul Mackerras <pau...@samba.org>
CC: Michael Ellerman <m...@ellerman.id.au>
CC: Dave Watson <davejwat...@fb.com>
CC: Ingo Molnar <mi...@redhat.com>
CC: "H. Peter Anvin" <h...@zytor.com>
CC: Andrea Parri <parri.and...@gmail.com>
CC: Russell King <li...@armlinux.org.uk>
CC: Greg Hackmann <ghackm...@google.com>
CC: Will Deacon <will.dea...@arm.com>
CC: David Sehr <s...@google.com>
CC: Linus Torvalds <torva...@linux-foundation.org>
CC: Arnd Bergmann <a...@arndb.de>
CC: x...@kernel.org
CC: linux-a...@vger.kernel.org
---
Changes since v1:
- Fix prototype of sync_core_before_usermode in generic code (missing
return type).
- Add linux/processor.h include to sched/core.c.
- Add ARCH_HAS_SYNC_CORE_BEFORE_USERMODE to init/Kconfig.
- Fix linux/processor.h ifdef to target
CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE rather than
ARCH_HAS_SYNC_CORE_BEFORE_USERMODE.
- Move empty static inline in processor.h to generic patch.
Changes since v2:
- Introduce arch/x86/include/asm/sync_core.h
- Don't sync_core when KPTI is enabled, and when invoked from irq and nmi
context.
- Note: v2 was reviewed by Thomas Gleixner, but changes were introduced
since.
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/sync_core.h | 28 ++++++++++++++++++++++++++++
2 files changed, 29 insertions(+)
create mode 100644 arch/x86/include/asm/sync_core.h
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 20da391b5f32..0b44c8dd0e95 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -61,6 +61,7 @@ config X86
select ARCH_HAS_SG_CHAIN
select ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_HAS_STRICT_MODULE_RWX
+ select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
select ARCH_HAS_UBSAN_SANITIZE_ALL
select ARCH_HAS_ZONE_DEVICE if X86_64
select ARCH_HAVE_NMI_SAFE_CMPXCHG
diff --git a/arch/x86/include/asm/sync_core.h b/arch/x86/include/asm/sync_core.h
new file mode 100644
index 000000000000..c67caafd3381
--- /dev/null
+++ b/arch/x86/include/asm/sync_core.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_SYNC_CORE_H
+#define _ASM_X86_SYNC_CORE_H
+
+#include <linux/preempt.h>
+#include <asm/processor.h>
+#include <asm/cpufeature.h>
+
+/*
+ * Ensure that a core serializing instruction is issued before returning
+ * to user-mode. x86 implements return to user-space through sysexit,
+ * sysrel, and sysretq, which are not core serializing.
+ */
+static inline void sync_core_before_usermode(void)
+{
+ /* With PTI, we unconditionally serialize before running user code. */
+ if (static_cpu_has(X86_FEATURE_PTI))
+ return;
+ /*
+ * Return from interrupt and NMI is done through iret, which is core
+ * serializing.
+ */
+ if (in_irq() || in_nmi())
+ return;
+ sync_core();
+}
+
+#endif /* _ASM_X86_SYNC_CORE_H */
--
2.11.0
