Re: [Xen-devel] [PATCH V3] vmx/nmi: Do not use self_nmi() in VMEXIT handler

[Tim Deegan <tim@xxxxxxx>]

At 09:58 +0000 on 28 Feb (1362045494), Jan Beulich wrote:
> >>> On 22.11.12 at 17:12, Jan Beulich wrote:
> >>>> On 22.11.12 at 17:05, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > > On 22/11/12 15:55, Jan Beulich wrote:
> > >>>>> On 22.11.12 at 16:37, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > >>> A quick solution would be to execute a noop function with
> > >>> run_in_exception_handler().  Alternatively, I can code enable_nmi() or
> > >>> so which does an inline iret to itself.  Which of these would you 
> > >>> prefer?
> > >> I would actually consider avoiding to run softirqs altogether in that
> > >> case, just like native Linux doesn't do any event or scheduler
> > >> processing in that case.
> > > 
> > > That would probably be the easiest solution.
> > > 
> > > I was already going to do the same for the rentrant NMI and MCE handling
> > > case (and also the process pending upcalls checking), due to the
> > > complexities of fixing the race condition at the end of the handler.
> > > 
> > > Unfortunately, I don't think I have time to look at this issue
> > > immediately, but if it is ok to wait till the beginning of next week, I
> > 
> > That's fine of course.
> 
> So that was 3 months ago, and we're likely going to need to do
> further unfixed releases if this won't move forward. Can you
> estimate whether you'll be able to get back to this?

Let's make a step in the right direction before 4.3, at least:

commit d278beed1df2d226911dce92295411018c9bba2f
Author: Tim Deegan <tim@xxxxxxx>
Date:   Thu Feb 28 12:42:15 2013 +0000

    vmx: handle NMIs before re-enabling interrupts.
    
    Also, switch to calling do_nmi() and explicitly re-enabling NMIs
    rather than raising a fake NMI and relying on the NMI processing to
    IRET, since that handling code is likely to change a fair amount in
    future.
    
    Signed-off-by: Tim Deegan <tim@xxxxxxx>

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 5378928..462bb0f 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2313,6 +2313,13 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
         vector = intr_info & INTR_INFO_VECTOR_MASK;
         if ( vector == TRAP_machine_check )
             do_machine_check(regs);
+        if ( vector == TRAP_machine_check
+             && ((intr_info & INTR_INFO_INTR_TYPE_MASK) ==
+                 (X86_EVENTTYPE_NMI << 8)) )
+        {
+            do_nmi(regs);
+            enable_nmis();
+        }
         break;
     case EXIT_REASON_MCE_DURING_VMENTRY:
         do_machine_check(regs);
@@ -2486,7 +2493,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
                  (X86_EVENTTYPE_NMI << 8) )
                 goto exit_and_crash;
             HVMTRACE_0D(NMI);
-            self_nmi(); /* Real NMI, vector 2: normal processing. */
+            /* Already handled above. */
             break;
         case TRAP_machine_check:
             HVMTRACE_0D(MCE);

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