x86/traps: Handle #DB for bus lock
Bus locks degrade performance for the whole system, not just for the CPU
that requested the bus lock. Two CPU features "#AC for split lock" and
"#DB for bus lock" provide hooks so that the operating system may choose
one of several mitigation strategies.
#AC for split lock is already implemented. Add code to use the #DB for
bus lock feature to cover additional situations with new options to
mitigate.
split_lock_detect=
#AC for split lock #DB for bus lock
off Do nothing Do nothing
warn Kernel OOPs Warn once per task and
Warn once per task and and continues to run.
disable future checking
When both features are
supported, warn in #AC
fatal Kernel OOPs Send SIGBUS to user.
Send SIGBUS to user
When both features are
supported, fatal in #AC
ratelimit:N Do nothing Limit bus lock rate to
N per second in the
current non-root user.
Default option is "warn".
Hardware only generates #DB for bus lock detect when CPL>0 to avoid
nested #DB from multiple bus locks while the first #DB is being handled.
So no need to handle #DB for bus lock detected in the kernel.
#DB for bus lock is enabled by bus lock detection bit 2 in DEBUGCTL MSR
while #AC for split lock is enabled by split lock detection bit 29 in
TEST_CTRL MSR.
Both breakpoint and bus lock in the same instruction can trigger one #DB.
The bus lock is handled before the breakpoint in the #DB handler.
Delivery of #DB for bus lock in userspace clears DR6[11], which is set by
the #DB handler right after reading DR6.
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20210322135325.682257-3-fenghua.yu@intel.com
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index da78ccb..0d7fc0e 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -41,12 +41,13 @@ unsigned int x86_family(unsigned int sig);
unsigned int x86_model(unsigned int sig);
unsigned int x86_stepping(unsigned int sig);
#ifdef CONFIG_CPU_SUP_INTEL
-extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
+extern void __init sld_setup(struct cpuinfo_x86 *c);
extern void switch_to_sld(unsigned long tifn);
extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
extern bool handle_guest_split_lock(unsigned long ip);
+extern void handle_bus_lock(struct pt_regs *regs);
#else
-static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
+static inline void __init sld_setup(struct cpuinfo_x86 *c) {}
static inline void switch_to_sld(unsigned long tifn) {}
static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
{
@@ -57,6 +58,8 @@ static inline bool handle_guest_split_lock(unsigned long ip)
{
return false;
}
+
+static inline void handle_bus_lock(struct pt_regs *regs) {}
#endif
#ifdef CONFIG_IA32_FEAT_CTL
void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 546d6ec..32c496f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -265,6 +265,7 @@
#define DEBUGCTLMSR_LBR (1UL << 0) /* last branch recording */
#define DEBUGCTLMSR_BTF_SHIFT 1
#define DEBUGCTLMSR_BTF (1UL << 1) /* single-step on branches */
+#define DEBUGCTLMSR_BUS_LOCK_DETECT (1UL << 2)
#define DEBUGCTLMSR_TR (1UL << 6)
#define DEBUGCTLMSR_BTS (1UL << 7)
#define DEBUGCTLMSR_BTINT (1UL << 8)
