From owner-freebsd-hackers@FreeBSD.ORG Tue Apr 7 14:28:50 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2BC8E106564A; Tue, 7 Apr 2009 14:28:50 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id EFC638FC15; Tue, 7 Apr 2009 14:28:49 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 8987946B39; Tue, 7 Apr 2009 10:28:49 -0400 (EDT) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id 76B1C8A04B; Tue, 7 Apr 2009 10:28:48 -0400 (EDT) From: John Baldwin To: Sergey Babkin Date: Tue, 7 Apr 2009 09:21:13 -0400 User-Agent: KMail/1.9.7 References: <1366225354.253456.1238948619308.JavaMail.root@vms124.mailsrvcs.net> <200904061342.22000.jhb@freebsd.org> <49DAC4A1.589A5FE@verizon.net> In-Reply-To: <49DAC4A1.589A5FE@verizon.net> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200904070921.14294.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Tue, 07 Apr 2009 10:28:48 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=0.1 required=4.2 tests=RDNS_NONE autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx Cc: freebsd-hackers@freebsd.org, Ivan Voras Subject: Re: Patch for MS Hyper V (virtualization) X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 07 Apr 2009 14:28:50 -0000 On Monday 06 April 2009 11:12:33 pm Sergey Babkin wrote: > John Baldwin wrote: > >=20 > > On Monday 06 April 2009 1:07:38 pm Ivan Voras wrote: > > > 2009/4/6 John Baldwin : > > > > On Sunday 05 April 2009 12:23:39 pm Sergey Babkin wrote: > > > > > > > Hmm, the problem is we need to be able to write to BARs to size the= m.=20 =D0=B1 Any > > OS > > > > needs to be able to do this to know what address space regions are= =20 being > > > > decoded by devices. =D0=B1 We can't avoid writing to BARs. > > > > > > I have only vague idea what BARs are and if it's the correct diagnosis > > > in this case, but the fact is that other operating systems (Windows, > > > Linux tested) work, so either there is a way around it or the original > > > premise is wrong-ish. > >=20 > > Every OS writes to BARs to size them during boot. It's the defined=20 procedure > > for sizing them. A BAR is a base address register, and it is how a PCI > > device gets memory and I/O port resources. OS (or BIOS) writes a start= ing > > address into the register to tell the PCI device where a given > > resource "starts". >=20 > The OS doesn't have to write to the BAR if BIOS has already > done it. And the BIOS in the Hyper-V VM is obviously special, > so it doesn't trip on iself.=20 Yes it does because we don't know how _big_ the BAR is. The OS has to know= if=20 the device is decoding 1MB or 64KB because we need to reserve the entire=20 window to prevent any other devices from using it. We don't just write the= =20 existing value, we write all 1's to it and read it back. The lower N=20 bits "stick" at zero and we use that to figure out the BAR's size. See=20 pci_add_map() in sys/dev/pci/pci.c > Anyway, as far as I can tell, it's only the base register of=20 > the simulated DEC21140 device that has this issue, so it's=20 > quite possible that the bug is in that device's simulator.=20 >=20 > I've attached a modified patch that checks conservatively for this > precise situation, so it should not break compatibility with > anything else. I've tested it on Hyper-V. Can you test unmodified FreeBSD 8 on Hyper-V? It has an extra fix relative= to=20 7 to disable decoding via the PCI command register while sizing BARs that m= ay=20 address this. =2D-=20 John Baldwin