Merge tag 'x86-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Thomas Gleixner:
"A set of three patches to fix the fallout of the newly added split
lock detection feature.
It addressed the case where a KVM guest triggers a split lock #AC and
KVM reinjects it into the guest which is not prepared to handle it.
Add proper sanity checks which prevent the unconditional injection
into the guest and handles the #AC on the host side in the same way as
user space detections are handled. Depending on the detection mode it
either warns and disables detection for the task or kills the task if
the mode is set to fatal"
* tag 'x86-urgent-2020-04-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
KVM: VMX: Extend VMXs #AC interceptor to handle split lock #AC in guest
KVM: x86: Emulate split-lock access as a write in emulator
x86/split_lock: Provide handle_guest_split_lock()
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index ff6f3ca..dd17c2d 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -44,6 +44,7 @@
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) {}
@@ -51,5 +52,10 @@
{
return false;
}
+
+static inline bool handle_guest_split_lock(unsigned long ip)
+{
+ return false;
+}
#endif
#endif /* _ASM_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 9a26e97..bf08d45 100644
--- 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 @@
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 @@
*/
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;
}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8959514..8305097 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4588,6 +4588,26 @@
return 1;
}
+/*
+ * If the host has split lock detection disabled, then #AC is
+ * unconditionally injected into the guest, which is the pre split lock
+ * detection behaviour.
+ *
+ * If the host has split lock detection enabled then #AC is
+ * only injected into the guest when:
+ * - Guest CPL == 3 (user mode)
+ * - Guest has #AC detection enabled in CR0
+ * - Guest EFLAGS has AC bit set
+ */
+static inline bool guest_inject_ac(struct kvm_vcpu *vcpu)
+{
+ if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+ return true;
+
+ return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) &&
+ (kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+}
+
static int handle_exception_nmi(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -4653,9 +4673,6 @@
return handle_rmode_exception(vcpu, ex_no, error_code);
switch (ex_no) {
- case AC_VECTOR:
- kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
- return 1;
case DB_VECTOR:
dr6 = vmcs_readl(EXIT_QUALIFICATION);
if (!(vcpu->guest_debug &
@@ -4684,6 +4701,20 @@
kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
kvm_run->debug.arch.exception = ex_no;
break;
+ case AC_VECTOR:
+ if (guest_inject_ac(vcpu)) {
+ kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
+ return 1;
+ }
+
+ /*
+ * Handle split lock. Depending on detection mode this will
+ * either warn and disable split lock detection for this
+ * task or force SIGBUS on it.
+ */
+ if (handle_guest_split_lock(kvm_rip_read(vcpu)))
+ return 1;
+ fallthrough;
default:
kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
kvm_run->ex.exception = ex_no;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 027dfd2..3bf2ecaf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5839,6 +5839,7 @@
{
struct kvm_host_map map;
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
+ u64 page_line_mask;
gpa_t gpa;
char *kaddr;
bool exchanged;
@@ -5853,7 +5854,16 @@
(gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
goto emul_write;
- if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
+ /*
+ * Emulate the atomic as a straight write to avoid #AC if SLD is
+ * enabled in the host and the access splits a cache line.
+ */
+ if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+ page_line_mask = ~(cache_line_size() - 1);
+ else
+ page_line_mask = PAGE_MASK;
+
+ if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask))
goto emul_write;
if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))
