From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47080) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WK934-0001rd-AW for qemu-devel@nongnu.org; Sun, 02 Mar 2014 11:15:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WK92v-0000Dt-1M for qemu-devel@nongnu.org; Sun, 02 Mar 2014 11:15:30 -0500 Received: from mail-qg0-x232.google.com ([2607:f8b0:400d:c04::232]:60252) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WK92u-0000DT-OI for qemu-devel@nongnu.org; Sun, 02 Mar 2014 11:15:20 -0500 Received: by mail-qg0-f50.google.com with SMTP id z60so8499702qgd.9 for ; Sun, 02 Mar 2014 08:15:19 -0800 (PST) Date: Sun, 2 Mar 2014 11:15:15 -0500 From: "Gabriel L. Somlo" Message-ID: <20140302161515.GA29049@foober.ini.cmu.edu> References: <20140228172343.GI17184@ERROL.INI.CMU.EDU> <20140228185719.GJ17184@ERROL.INI.CMU.EDU> <20140302145222.GE30372@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140302145222.GE30372@redhat.com> Subject: Re: [Qemu-devel] [RFC PATCH v2] qemu: x86: ignore ioapic polarity List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, agraf@suse.de On Sun, Mar 02, 2014 at 04:52:22PM +0200, Michael S. Tsirkin wrote: > On Fri, Feb 28, 2014 at 01:57:19PM -0500, Gabriel L. Somlo wrote: > > Both QEMU and KVM have already accumulated a significant number of > > optimizations based on the hard-coded assumption that ioapic polarity > > will always use the ActiveHigh convention, where the logical and > > physical states of level-triggered irq lines always match (i.e., > > active(asserted) == high == 1, inactive == low == 0). QEMU guests > > are expected to follow directions given via ACPI and configure the > > ioapic with polarity 0 (ActiveHigh). However, even when misbehaving > > guests (e.g. OS X <= 10.9) set the ioapic polarity to 1 (ActiveLow), > > QEMU will still use the ActiveHigh signaling convention when > > interfacing with the emulated ioapic. > > > > This patch modifies the emulated ioapic to completely ignore polarity > > as set by the guest OS, enabling misbehaving guests to work alongside > > those which comply with the ActiveHigh polarity specified by QEMU's > > ACPI tables. > > > > Signed-off-by: Gabriel L. Somlo > > > Acked-by: Michael S. Tsirkin > Reviewed-by: Michael S. Tsirkin > > > With this, we should be able to change ACPI to specify > active-low, which is closer to what real hardware does. > But as long as we don't I think there's no need for > compatibility with old machine types: we are not > breaking any behaviour that wasn't already broken. I only really saw ActiveLow on Apple machines' ACPI, though. Not sure what the latest-minute PC hardware does, but all late-2000's and early-2010's machines I've seen mostly have ActiveHigh in ACPI. I guess I'd leave ACPI ActiveHigh, these patches are about what happens when some stubborn guest OS decides to ignore ACPI :) Who knows, in another 5 years and two OS X versions they might start actually checking ACPI just like they started checking CPUID for monitor/mwait as of 10.8 :) But if the guest OS is well behaved, then logical == physical signaling (with ActiveHigh), and that's easier (at least for me) to wrap one's head around :) Thanks, --Gabriel > > > > --- > > > > > OK, this would "harmonize" TCG with KVM, in terms of acknowledging > > > the realities of hard-coded ActiveHigh behavior throughout the rest > > > of the code base. > > > > Now with a new and improved commit blurb :) > > > > Thanks, > > Gabriel > > > > hw/intc/ioapic.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c > > index 652dd47..b527932 100644 > > --- a/hw/intc/ioapic.c > > +++ b/hw/intc/ioapic.c > > @@ -93,9 +93,6 @@ static void ioapic_set_irq(void *opaque, int vector, int level) > > uint32_t mask = 1 << vector; > > uint64_t entry = s->ioredtbl[vector]; > > > > - if (entry & (1 << IOAPIC_LVT_POLARITY_SHIFT)) { > > - level = !level; > > - } > > if (((entry >> IOAPIC_LVT_TRIGGER_MODE_SHIFT) & 1) == > > IOAPIC_TRIGGER_LEVEL) { > > /* level triggered */ > > -- > > 1.8.1.4