RE: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the interrupt is not single-destination

[Wu, Feng]

> -----Original Message-----
> From: Radim Krcmár [mailto:rkrcmar@xxxxxxxxxx]
> Sent: Monday, January 25, 2016 10:06 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
> interrupt is not single-destination
> 
> 2016-01-25 12:26+0000, Wu, Feng:
> >> From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo
> >> It may be necessary because IRTE writes (128 bits) are not atomic.
> >
> > IRTE is updated atomically, I added the patch to support this. Please
> > refer to 344cb4e0b6f3a0dbef0643eacb4946338eb228c0.
> 
> I also think that SN bit is not affected by atomicity: if the IRTE could
> have been read half-updated while changing from posted to non-posted,
> then it wouldn't point to the correct PID, because its address is not
> within 64 bits, so the SN bit wouldn't matter.

Yes, like the comments in the commit, we should atomically update the
IRTE in PI case (PI -> non-PI, non-PI -> PI), without which, it cannot
guarantee the correctness, since 'pda' is not within 64 bits, like Radim
pointed out above.

Thanks,
Feng

> 
> IRTE invalidation seems important in VT-d ...