linux-kernel - Re: [PATCH LINUX v4] xen: event channel arrays are xen_ulong

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Date:	Tue, 19 Feb 2013 13:43:37 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Ian Campbell <ian.campbell@...rix.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	"Keir (Xen.org)" <keir@....org>, "Tim (Xen.org)" <tim@....org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH LINUX v4] xen: event channel arrays are xen_ulong_t and
 not unsigned long

On Tue, Feb 19, 2013 at 06:12:35PM +0000, Stefano Stabellini wrote:
> On Tue, 19 Feb 2013, Ian Campbell wrote:
> > On ARM we want these to be the same size on 32- and 64-bit.
> > 
> > This is an ABI change on ARM. X86 does not change.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> > Cc: Jan Beulich <JBeulich@...e.com>
> > Cc: Keir (Xen.org) <keir@....org>
> > Cc: Tim Deegan <tim@....org>
> > Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: xen-devel@...ts.xen.org
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ---
> > Changes since V3
> >   s/read_evtchn_pending_sel/xchg_xen_ulong/ in a comment.
> > Changes since V2
> >   Add comments about the correct bitops to use, and on the ordering/barrier
> >   requirements on xchg_xen_ulong.
> > Changes since V1
> >   use find_first_set not __ffs
> >   fix some more unsigned long -> xen_ulong_t
> >   use more generic xchg_xen_ulong instead of ...read_evtchn...
> 
> still doesn't apply to 3.8

Weird. It applied to my tree (stable/for-linus-3.9) without fuss.
> 
> 
> >         do {
> > -               unsigned long pending_words;
> > +               xen_ulong_t pending_words;
> > 
> >                 vcpu_info->evtchn_upcall_pending = 0;
> > 
> >                 if (__this_cpu_inc_return(xed_nesting_count) - 1)
> >                         goto out;
> > 
> > -#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
> > -               /* Clear master flag /before/ clearing selector flag. */
> > -               wmb();
> > -#endif
> > -               pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
> > +               /*
> > +                * Master flag must be /before/ clearing selector
> > +                * flag. xchg_xen_ulong must contain an appropriate
> > +                * barrier.
> > +                */
> 
> Master flag must be *cleared* ...
> 
> > +               pending_words = xchg_xen_ulong(&vcpu_info->evtchn_pending_sel, 0);
> > 
> >                 start_word_idx = __this_cpu_read(current_word_idx);
> >                 start_bit_idx = __this_cpu_read(current_bit_idx);
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