From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH v8 2/2] kvm: x86: hyperv: guest->host event signaling via
 eventfd
Date: Thu, 1 Feb 2018 14:20:19 +0100
Message-ID: <20180201132018.GA26932@flask>
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To: Roman Kagan <rkagan@virtuozzo.com>, kvm@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        "Denis V. Lunev" <den@openvz.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
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        David Hildenbrand <david@redhat.com>
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2018-02-01 15:45+0300, Roman Kagan:
> On Wed, Jan 31, 2018 at 07:18:12PM +0100, Radim Krčmář wrote:
> > 2018-01-31 16:56+0300, Roman Kagan:
> > I have completely missed this series in the past, sorry.
> 
> No wonder, everybody was too busy with all this Meltdown+Spectre
> stuff.
> 
> > > +	/*
> > > +	 * Per spec, bits 32-47 contain the extra "flag number".  However, we
> > > +	 * have no use for it, and in all known usecases it is zero, so just
> > > +	 * require it here.
> > > +	 */
> > 
> > The spec says:
> > 
> >   FlagNumber specifies the relative index of the event flag that the
> >   caller wants to set within the target SIEF area. This number is
> >   relative to the base flag number associated with the port.
> 
> This smells like an overdesign to me.  Anyway we've never seen non-zero
> FlagNumbers.  The guest code in Linux doesn't even define a way to pass
> such a FlagNumber.
> 
> > Don't we want to pass the flag into userspace?
> 
> To be future-proof in case there turns out to be a user for non-zero
> FlagNumber?  Makes sense, will respin with that.

Exactly, thanks!