Re: [Xen-devel] NMI delivery not correctly working

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 24/7/07 19:26, "Kaushik Barde" <Kaushik_Barde@xxxxxxxxxxx> wrote:

> Processor disables calls to subsequent NMIs till it receives next IRET
> instruction

Yes.

> (via masking of maskable interrupts).

No, since NMIs are, of course, not maskable by conventional means.

> I guess, what I am not clear about is how a fully-virtualized guest
> whould issue a IRET hypercall?

It's used just like any other hypercall. Guest jumps at the correct offset
into its hypercall transfer page.

 -- Keir

> -Kaushik
> 
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
> Sent: Tuesday, July 24, 2007 10:08 AM
> To: Christoph Egger; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] NMI delivery not correctly working
> 
> On 24/7/07 16:47, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:
> 
>> I know, there is a line "current->nmi_masked = 0;" in do_iret() in
>> xen/arch/x86/x86_(32|64)/traps.c, but this is actually never called
>> after NMI delivery.
> 
> Guests *must* use the iret hypercall when returning from their NMI
> handler.
> This is giving a virtualised equivalent of the 'NMI-blocking' latch
> implemented in x86 processors, which is reset by the IRET instruction.
> 
>  -- Keir
> 
> 
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