[vbox-dev] Chipset support for Message Signaled Interrupts (MSI)

Vilbig, Ric ric_vilbig at mentor.com
Thu Mar 24 23:11:15 UTC 2016

Now I have the opposite question.  Are IRQ type interrupts (as in PCI Config 0x3d IntPin) expected to work with ICH9?

I have a virtual PCI device which works with PIIX3 quite nicely using IRQ4 — a USB3 mass storage device.  But when plugged into the ICH9 VM the device is not detected within the guest, using IRQ1/2/3/4.

The guest must know the device is present, because it does lots of MMIO Rd/Wr to it, and then the device does some DMA, and raises an interrupt.  Everything looks quite similar between the ICH9 and PIIX3 case, except the former does nothing more after raising the interrupt, whereas the latter continues working with lots more DMA, interrupts, and a usable mass storage device in the guest.

From what I have found so far, the interrupt is passed down into PDM, but does not actually do anything, and dmesg in the guest says "can't derive routing for PCI INT n".


//  RicV

From: Ananth Pallapothu [mailto:apallapothu at gmail.com]
Sent: Monday, March 21, 2016 15:55
To: Vilbig, Ric
Cc: VirtualBox developer's list
Subject: Re: [vbox-dev] Chipset support for Message Signaled Interrupts (MSI)

MSI's came into existence after PIIX3.

Yes, if you need MSI you need to use ICH9.
PIIX3 doesn't support MSI
On Mar 21, 2016 6:43 PM, "Vilbig, Ric" <ric_vilbig at mentor.com<mailto:ric_vilbig at mentor.com>> wrote:
Hi Experts,

I posted the following on the VIrtualBox forum, but Perry recommended I contact you by the email list.

I am working on a custom PCI device model, plugged into VirtualBox via PDM. It's mostly working, lspci for example shows it's present. But I am having a problem with Message Signaled Interrupts (MSI).

The following quote from Ch.3 of the VirtualBox User Manual implies that the ICP9 chipset must be used for MSI support, and I have seen supporting evidence in web searches and VBox source code (OSE 5.0.16 tarball).

“...VirtualBox 4.0 introduced an emulation of the more modern ICH9 chipset, which supports PCI express,
three PCI buses, PCI-to-PCI bridges and Message Signaled Interrupts (MSI)...”

Can someone confirm or refute with certainty that the PIIX3 chipset does not support MSI and ICH9 is required for device models using MSI?

How worried should I be about this excerpt from the same paragraph? A quick test of ICH9 VM did not go well. I've actually tried with Fedora 23, Fedora 18 and Ubuntu 14 guests (all 64-bit) without success, but not yet dug into it because this quote worries me.

“Note that the ICH9 support is experimental and not recommended for guest operating systems which do not require it.”

Thanks in advance for your help.


Ric Vilbig
Mentor Graphics, Emulation Division
46871 Bayside Parkway, Fremont CA, 94538
Phone:  510-354-7360<tel:510-354-7360>
Mobile: 408-529-2365<tel:408-529-2365>
email:  ric_vilbig at mentor.com<mailto:ric_vilbig at mentor.com>

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