[Xen-changelog] [xen-unstable] vmx: avoid taking locks with irqs disabled

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1224513114 -3600
# Node ID 824892134573b05573ca1945757bb2a99e220a02
# Parent  c4be040bef6faa4a1eae4ce71636cc1ae88a9f35
vmx: avoid taking locks with irqs disabled

Shuffle the bits of the vmexit handler that run with EFLAGS.IF == 0 up
to the top.  Otherwise we end up calling spin_lock() with interrupts
disabled, which can deadlock against the time-synchronization
rendezvous code.

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff -r c4be040bef6f -r 824892134573 xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Mon Oct 20 15:22:58 2008 +0100
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Mon Oct 20 15:31:54 2008 +0100
@@ -2056,8 +2056,12 @@ asmlinkage void vmx_vmexit_handler(struc
 
     perfc_incra(vmexits, exit_reason);
 
-    if ( exit_reason != EXIT_REASON_EXTERNAL_INTERRUPT )
-        local_irq_enable();
+    /* Handle the interrupt we missed before allowing any more in. */
+    if ( exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT )
+        vmx_do_extint(regs);
+
+    /* Now enable interrupts so it's safe to take locks. */
+    local_irq_enable();
 
     if ( unlikely(exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) )
         return vmx_failed_vmentry(exit_reason, regs);
@@ -2185,7 +2189,7 @@ asmlinkage void vmx_vmexit_handler(struc
         break;
     }
     case EXIT_REASON_EXTERNAL_INTERRUPT:
-        vmx_do_extint(regs);
+        /* Already handled above. */
         break;
     case EXIT_REASON_TRIPLE_FAULT:
         hvm_triple_fault();

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