Date: Mon, 06 Apr 2009 23:12:33 -0400 From: Sergey Babkin <babkin@verizon.net> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org, Ivan Voras <ivoras@freebsd.org> Subject: Re: Patch for MS Hyper V (virtualization) Message-ID: <49DAC4A1.589A5FE@verizon.net> References: <1366225354.253456.1238948619308.JavaMail.root@vms124.mailsrvcs.net> <200904061154.19601.jhb@freebsd.org> <9bbcef730904061007y66a8440al3c43a6a6b6cd6ed6@mail.gmail.com> <200904061342.22000.jhb@freebsd.org>
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John Baldwin wrote:
>
> On Monday 06 April 2009 1:07:38 pm Ivan Voras wrote:
> > 2009/4/6 John Baldwin <jhb@freebsd.org>:
> > > 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 them. Â Any
> OS
> > > needs to be able to do this to know what address space regions are being
> > > decoded by devices. Â 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.
>
> Every OS writes to BARs to size them during boot. It's the defined 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 starting
> address into the register to tell the PCI device where a given
> resource "starts".
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.
Anyway, as far as I can tell, it's only the base register of
the simulated DEC21140 device that has this issue, so it's
quite possible that the bug is in that device's simulator.
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.
-SB
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--- dev/pci/pci.c.0 2009-04-06 21:35:26.000000000 +0000
+++ dev/pci/pci.c 2009-04-06 22:43:08.000000000 +0000
@@ -3590,6 +3590,18 @@
struct pci_devinfo *dinfo = device_get_ivars(child);
pcicfgregs *cfg = &dinfo->cfg;
+ /* A workaround for Hyper-V that hangs on VM stop
+ * if the base address register of the 21140 simulator is written;
+ * since on Hyper-V the value written is the same as the one
+ * already in the register, it can be simply skipped.
+ * 0x1011: DEC, 0x0009: 21140 */
+ if (dinfo->cfg.vendor == 0x1011 && dinfo->cfg.device == 0x0009) {
+ if (reg == PCIR_BARS
+ && (val & ~3) == (PCIB_READ_CONFIG(device_get_parent(dev),
+ cfg->bus, cfg->slot, cfg->func, reg, width) & ~3) )
+ return;
+ }
+
PCIB_WRITE_CONFIG(device_get_parent(dev),
cfg->bus, cfg->slot, cfg->func, reg, val, width);
}
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