From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754010Ab2DTQrD (ORCPT ); Fri, 20 Apr 2012 12:47:03 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:22491 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752593Ab2DTQrB (ORCPT ); Fri, 20 Apr 2012 12:47:01 -0400 Date: Fri, 20 Apr 2012 12:41:51 -0400 From: Konrad Rzeszutek Wilk To: Ian Campbell Cc: Lin Ming , Andrew Cooper , "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall Message-ID: <20120420164150.GC31062@phenom.dumpdata.com> References: <1334913957.2863.1.camel@hp6530s> <4F913340.4000202@citrix.com> <1334920396.2863.16.camel@hp6530s> <1334925508.28331.63.camel@zakaz.uk.xensource.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1334925508.28331.63.camel@zakaz.uk.xensource.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet21.oracle.com [141.146.126.237] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090204.4F9192FD.000E,ss=1,re=0.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 20, 2012 at 01:38:28PM +0100, Ian Campbell wrote: > On Fri, 2012-04-20 at 12:13 +0100, Lin Ming wrote: > > On Fri, 2012-04-20 at 10:58 +0100, Andrew Cooper wrote: > > > On 20/04/12 10:25, Lin Ming wrote: > > > > Implements xen_io_apic_read with hypercall, so it returns proper IO-APIC > > > > information instead of fabricated one. > > > > > > > > Signed-off-by: Lin Ming > > > > --- > > > > arch/x86/xen/apic.c | 16 +++++++++++----- > > > > 1 files changed, 11 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c > > > > index aee16ab..f1f392d 100644 > > > > --- a/arch/x86/xen/apic.c > > > > +++ b/arch/x86/xen/apic.c > > > > @@ -1,14 +1,20 @@ > > > > #include > > > > #include > > > > +#include > > > > +#include > > > > +#include > > > > > > > > unsigned int xen_io_apic_read(unsigned apic, unsigned reg) > > > > { > > > > - if (reg == 0x1) > > > > - return 0x00170020; > > > > - else if (reg == 0x0) > > > > - return apic << 24; > > > > + struct physdev_apic apic_op; > > > > + int ret; > > > > > > > > - return 0xff; > > > > + apic_op.apic_physbase = mpc_ioapic_addr(apic); > > > > + apic_op.reg = reg; > > > > + ret = HYPERVISOR_physdev_op(PHYSDEVOP_apic_read, &apic_op); > > > > + if (ret) > > > > + return ret; > > > > + return apic_op.value; > > > > > > Hypercall ret errors are negative, yet this function is unsigned. Given > > > that the previous function had no possible way to fail, perhaps on error > > > you should fake up the values as before. > > > > How about return -1 on error? > > The calling function can check -1 for error. > > Isn't -1 potentially (at least theoretically) a valid value to read from > one of these registers? Yeah, but then we are back to crashing at bootup (with dom0) :-) Perhaps the fallback is to emulate (so retain some of the original code) as we have been since .. uh 3.0? > > Under what circumstances can these hypercalls fail? Would a BUG_ON be > appropriate/ > > > unsigned int ret = apic_read(...); > > if (ret == -1) > > //handle error. > > > > Thanks, > > Lin Ming > > > > > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@lists.xen.org > > http://lists.xen.org/xen-devel > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel