Re: [Xen-devel] [SVM][PATCH] fix NMI vmexit handling

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 Jul 2006, at 20:58, Woller, Thomas wrote:

> Attached SVM patch fixes a problem when an NMI is intercepted while
> running an SVM guest.
> Basically the NMI handler (do_nmi()) was being called twice, once when
> global interrupts was enabled, and then second when the vmexit nmi
> handler executed.
> This patch moves enablement of the global interrupts (STGI) from the 
> asm
> exits.S files to the vmexit handler (svm.c), and then enables 
> interrupts
> after the do_nmi() handling.
How does moving the STGI fix this double-nmi problem? The reference 
manual says that external interrupts are 'held pending' until delivery 
is enabled by the VMM. I can't see that do_nmi() does anything that 
would cause that pending status to be reset (local APIC isn't EOI'ed, 
or anything like that) and so I would expect that you would still get 
an NMI when STGI is executed, and all you've done is switch the order 
(the explicit call to do_nmi() happens before the STGI_triggered one). 
Am I wrong?
Another thing: the code you have under case VMEXIT_INTR, which raises 
schedule softirq, seems pointless. All interrupt work will happen in 
proper interrupt context triggered on STGI. Should the code under 
VMEXIT_INTR simply be removed?
 -- Keir


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