[patch 1/3] x86/split_lock: Provide handle_guest_split_lock()

From: Thomas Gleixner
Date: Fri Apr 10 2020 - 07:56:10 EST


From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Without at least minimal handling for split lock detection induced #AC, VMX
will just run into the same problem as the VMWare hypervisor, which was
reported by Kenneth.

It will inject the #AC blindly into the guest whether the guest is prepared
or not.

Provide a function for guest mode which acts depending on the host SLD
mode. If mode == sld_warn, treat it like user space, i.e. emit a warning
disable SLD and mark the task accordingly. Otherwise force SIGBUS.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "Kenneth R. Crudup" <kenny@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>

---
arch/x86/include/asm/cpu.h | 1 +
arch/x86/kernel/cpu/intel.c | 33 ++++++++++++++++++++++++++++-----
2 files changed, 29 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -44,6 +44,7 @@ unsigned int x86_stepping(unsigned int s
extern void __init cpu_set_core_cap_bits(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);
#else
static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
static inline void switch_to_sld(unsigned long tifn) {}
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -21,6 +21,7 @@
#include <asm/elf.h>
#include <asm/cpu_device_id.h>
#include <asm/cmdline.h>
+#include <asm/traps.h>

#ifdef CONFIG_X86_64
#include <linux/topology.h>
@@ -1066,13 +1067,10 @@ static void split_lock_init(void)
split_lock_verify_msr(sld_state != sld_off);
}

-bool handle_user_split_lock(struct pt_regs *regs, long error_code)
+static void split_lock_warn(unsigned long ip)
{
- if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
- return false;
-
pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
- current->comm, current->pid, regs->ip);
+ current->comm, current->pid, ip);

/*
* Disable the split lock detection for this task so it can make
@@ -1081,6 +1079,31 @@ bool handle_user_split_lock(struct pt_re
*/
sld_update_msr(false);
set_tsk_thread_flag(current, TIF_SLD);
+}
+
+bool handle_guest_split_lock(unsigned long ip)
+{
+ if (sld_state == sld_warn) {
+ split_lock_warn(ip);
+ return true;
+ }
+
+ pr_warn_once("#AC: %s/%d %s split_lock trap at address: 0x%lx\n",
+ current->comm, current->pid,
+ sld_state == sld_fatal ? "fatal" : "bogus", ip);
+
+ current->thread.error_code = 0;
+ current->thread.trap_nr = X86_TRAP_AC;
+ force_sig_fault(SIGBUS, BUS_ADRALN, NULL);
+ return false;
+}
+EXPORT_SYMBOL_GPL(handle_guest_split_lock);
+
+bool handle_user_split_lock(struct pt_regs *regs, long error_code)
+{
+ if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
+ return false;
+ split_lock_warn(regs->ip);
return true;
}