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x86/kvm: Fix broken irq restoration in kvm_wait
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After commit 997acaf (lockdep: report broken irq restoration), the guest
splatting below during boot:

 raw_local_irq_restore() called with IRQs enabled
 WARNING: CPU: 1 PID: 169 at kernel/locking/irqflag-debug.c:10 warn_bogus_irq_restore+0x26/0x30
 Modules linked in: hid_generic usbhid hid
 CPU: 1 PID: 169 Comm: systemd-udevd Not tainted 5.11.0+ #25
 RIP: 0010:warn_bogus_irq_restore+0x26/0x30
 Call Trace:
  kvm_wait+0x76/0x90
  __pv_queued_spin_lock_slowpath+0x285/0x2e0
  do_raw_spin_lock+0xc9/0xd0
  _raw_spin_lock+0x59/0x70
  lockref_get_not_dead+0xf/0x50
  __legitimize_path+0x31/0x60
  legitimize_root+0x37/0x50
  try_to_unlazy_next+0x7f/0x1d0
  lookup_fast+0xb0/0x170
  path_openat+0x165/0x9b0
  do_filp_open+0x99/0x110
  do_sys_openat2+0x1f1/0x2e0
  do_sys_open+0x5c/0x80
  __x64_sys_open+0x21/0x30
  do_syscall_64+0x32/0x50
  entry_SYSCALL_64_after_hwframe+0x44/0xae

The new consistency checking,  expects local_irq_save() and
local_irq_restore() to be paired and sanely nested, and therefore expects
local_irq_restore() to be called with irqs disabled.
The irqflags handling in kvm_wait() which ends up doing:

	local_irq_save(flags);
	safe_halt();
	local_irq_restore(flags);

instead triggers it.  This patch fixes it by using
local_irq_disable()/enable() directly.

Cc: Thomas Gleixner <[email protected]>
Reported-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
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Wanpeng Li authored and bonzini committed Mar 18, 2021
1 parent c2162e1 commit f4e61f0
Showing 1 changed file with 10 additions and 13 deletions.
23 changes: 10 additions & 13 deletions arch/x86/kernel/kvm.c
Original file line number Diff line number Diff line change
Expand Up @@ -836,28 +836,25 @@ static void kvm_kick_cpu(int cpu)

static void kvm_wait(u8 *ptr, u8 val)
{
unsigned long flags;

if (in_nmi())
return;

local_irq_save(flags);

if (READ_ONCE(*ptr) != val)
goto out;

/*
* halt until it's our turn and kicked. Note that we do safe halt
* for irq enabled case to avoid hang when lock info is overwritten
* in irq spinlock slowpath and no spurious interrupt occur to save us.
*/
if (arch_irqs_disabled_flags(flags))
halt();
else
safe_halt();
if (irqs_disabled()) {
if (READ_ONCE(*ptr) == val)
halt();
} else {
local_irq_disable();

out:
local_irq_restore(flags);
if (READ_ONCE(*ptr) == val)
safe_halt();

local_irq_enable();
}
}

#ifdef CONFIG_X86_32
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