[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen: vmx: Use an INT 2 call to process real NMI's instead of self_nmi() in VMEXIT handler
At 13:29 +0000 on 13 Nov (1352813350), Ian Campbell wrote: > On Tue, 2012-11-13 at 13:21 +0000, Malcolm Crossley wrote: > > The self_nmi() code cause's an NMI to be triggered by sending an APIC > > message > > to the local processor. Unfortunately there is a delay in the delivery of > > the > > APIC message and we may already have re-entered the HVM guest by the time > > the > > NMI is taken. This results in the VMEXIT code calling the self_nmi() > > function > > again. We have seen hundreds of iterations of this VMEXIT/VMENTER loop > > before > > the HVM guest resumes normal operation. > > > > Volume 3 Chapter 27 Section 1 of the Intel SDM states: > > > > An NMI causes subsequent NMIs to be blocked, but only after the VM exit > > completes. > > > > So we believe it is safe to directly invoke the INT call as NMI's should > > already be blocked. > > > > The INT 2 call will perform an IRET which will unblock later calls to the > > NMI > > handler, according to Intel SDM Volume 3 Chapter 6.7.1. > > > > Signed-off-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> > > Acked-by: Tim Deegan <tim@xxxxxxx> > > > > diff -r 62885b3c34c8 -r e1fbee58b25c xen/arch/x86/hvm/vmx/vmx.c > > --- a/xen/arch/x86/hvm/vmx/vmx.c > > +++ b/xen/arch/x86/hvm/vmx/vmx.c > > @@ -2442,7 +2442,7 @@ void vmx_vmexit_handler(struct cpu_user_ > > (X86_EVENTTYPE_NMI << 8) ) > > goto exit_and_crash; > > HVMTRACE_0D(NMI); > > - self_nmi(); /* Real NMI, vector 2: normal processing. */ > > + asm("int $2"); /* Real NMI, vector 2: normal processing. */ > > asm volatile("...") > > I think? Otherwise this could potentially get hoisted up Good catch. Hoisted would be fine, but it could also be entirely discarded. :) > Do we need any clobbers? Specifically I'm thinking of memory since > taking an int2 ought to preserve register state. I don't think so - nothing on this path depends on the actual behaviour of the NMI handler. Tim. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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