[xen stable-4.18] x86/vmx: Fix IRQ handling for EXIT_REASON_INIT

[patchbot@xxxxxxx]

commit 4cc0f88c42f374c7a8e2d05e38777fa18619482e
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Feb 1 17:59:57 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 1 17:59:57 2024 +0100

    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@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: d1f8883aebe00f6a9632d77ab0cd5c6d02c9cbe4
    master date: 2024-01-18 20:59:06 +0000
---
 xen/arch/x86/hvm/vmx/vmx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 1edc7f1e91..964891934b 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -4100,7 +4100,7 @@ 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. */
@@ -4385,6 +4385,7 @@ 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:
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18