x86/vmx: Fix IRQ handling for EXIT_REASON_INIT

When receiving an INIT, a prior bugfix tried to ignore the INIT and continue
onwards.

Unfortunately it's not safe to return at that point in vmx_vmexit_handler().
Just out of context in the first hunk is a local_irqs_enabled() which is
depended-upon by the return-to-guest path, causing the following checklock
failure in debug builds:

  (XEN) Error: INIT received - ignoring
  (XEN) CHECKLOCK FAILURE: prev irqsafe: 0, curr irqsafe 1
  (XEN) Xen BUG at common/spinlock.c:132
  (XEN) ----[ Xen-4.19-unstable  x86_64  debug=y  Tainted:     H  ]----
  ...
  (XEN) Xen call trace:
  (XEN)    [<ffff82d040238e10>] R check_lock+0xcd/0xe1
  (XEN)    [<ffff82d040238fe3>] F _spin_lock+0x1b/0x60
  (XEN)    [<ffff82d0402ed6a8>] F pt_update_irq+0x32/0x3bb
  (XEN)    [<ffff82d0402b9632>] F vmx_intr_assist+0x3b/0x51d
  (XEN)    [<ffff82d040206447>] F vmx_asm_vmexit_handler+0xf7/0x210

Luckily, this is benign in release builds.  Accidentally having IRQs disabled
when trying to take an IRQs-on lock isn't a deadlock-vulnerable pattern.

Drop the problematic early return.  In hindsight, it's wrong to skip other
normal VMExit steps.

Fixes: b1f11273d5a7 ("x86/vmx: Don't spuriously crash the domain when INIT is received")
Reported-by: Reima ISHII <ishiir@g.ecc.u-tokyo.ac.jp>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: d1f8883aebe00f6a9632d77ab0cd5c6d02c9cbe4
master date: 2024-01-18 20:59:06 +0000

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 072288a5ef11ef62bd6568e56dad74dfa339c01f..31f4a861c650c368a053f55824281239dcc6bc80 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -4037,7 +4037,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
 
     case EXIT_REASON_INIT:
         printk(XENLOG_ERR "Error: INIT received - ignoring\n");
-        return; /* Renter the guest without further processing */
+        break;
     }
 
     /* Now enable interrupts so it's safe to take locks. */
@@ -4323,6 +4323,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         break;
     }
     case EXIT_REASON_EXTERNAL_INTERRUPT:
+    case EXIT_REASON_INIT:
         /* Already handled above. */
         break;
     case EXIT_REASON_TRIPLE_FAULT: