linux-kernel - Re: [PATCH v2 2/3] x86/kvm/hyper-v: remove stale entries from vec_bitmap/auto_eoi

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Date:   Fri, 9 Mar 2018 16:45:16 +0100
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        "Denis V . Lunev" <den@...nvz.org>
Subject: Re: [PATCH v2 2/3] x86/kvm/hyper-v: remove stale entries from
 vec_bitmap/auto_eoi_bitmap on vector change

2018-03-09 16:21+0100, Vitaly Kuznetsov:
> Radim Krčmář <rkrcmar@...hat.com> writes:
> > This looks like it solves the problem when we get two SINTs with the
> > same vector back-to-back , but shouldn't these bits really be cleared on
> > EOI (either auto or manual)?
> 
> Hmm,
> 
> I was trying to address the following issue: guest programs SynIC's
> SINTx with some vector but later re-programs it with a different
> one. Without the patch synic->vec_bitmap and synic->auto_eoi_bitmap keep
> stale data. If there's no concurrent interrupt than we're safe, but what
> happens if there is one...
> 
> kvm_hv_synic_send_eoi() already goes through all SINTx but we already
> updated vector so it won't find any. We could've added something like
> 'old_vector' but what if the request with this vector came _after_ we
> re-programed SynIC (and, so, it wasn't meant to be serviced by SynIC?)?

I now read that TLFS puts the responsitiblity on guest OS when toggling
auto-EOI, so let's assume that the OS is to blame for disabling/changing
vectors with pending interrupts as well.

Applied all, thanks.