[vbox-dev] ICH9 BAR5 access

Michal Necasek michal.necasek at oracle.com
Wed Aug 19 15:05:07 GMT 2015

Yes, I agree that this does not appear to be MSI related at all. I still don't quite understand the utility of working with old source code with known bugs. What's more, we can't fix old versions, and you'll almost certainly need either us to fix something or tell us what to fix it. But if you really want to start with an old version then that's of course your choice. 

I saw two VGA devices listed in your lspci output. I'm not saying it has to cause problems, but it is an untried/untested configuration. 

With EFI, you should expect the firmware to initialize the BARs. That is the significant difference compared to the "classic" BIOS in VirtualBox. 

Comparing DevPciIch9.cpp with DevPCI.cpp is the right thing to do, although there are intentional differences. The problem is very likely there. I'd suggest tracing ich9pciUpdateMappings() as all BAR changes should go through there. 

I can also tell you right away that I have no idea how well 64-bit BARs work because that's a feature more or less totally unused by the VirtualBox devices (it only comes into play with PCI passthrough, which is very rarely used). FYI, the device with most BARs (six) that we have is AHCI. 

I'm afraid I don't have any more specific suggestions because I don't know what your code is doing. If you can distill the problem into a testcase that we can look at, we'd be happy to. 


----- Original Message ----- 
From: apallapothu at gmail.com 
To: michal.necasek at oracle.com 
Cc: vbox-dev at virtualbox.org 
Sent: Wednesday, August 19, 2015 2:46:55 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna 
Subject: Re: [vbox-dev] ICH9 BAR5 access 

Hi Michal, 

I successfully used all BAR's with PIIX3 chipset. 

Correct, MSI supporting is the piece forcing me move to ICH9. I understand changes have been made to MSI since then, but this particular issue doesn't seem to have anything to do with MSI, right? I was looking more interms of getting basic functionality of all BAR's on ICH9 working first before upgrading myself to latest VirtualBox. 

My device is the VGA device. Did you find any duplicate mention somewhere ? 

I will try with EFI, see if it makes any difference. What should I expect with this change ? Can you please recommend expected debug points in the source code that first invoke ICH9 BAR5 source code ? VBoxManage modifyvm --name VM_name ----firmware efi 

I tried to compare basic function calls between ICH9 vs PIIX3, but eventually got lost at some point. Did find some similarities using gdb EM.cpp -> EMHM.cpp -> HM.cpp -> DevPciIch9.cpp / DevPCI.cpp. 

Suggestions / recommendations would really help. 


On Wed, Aug 19, 2015 at 7:51 AM, Michal Necasek < michal.necasek at oracle.com > wrote: 

Hi Ananth, 

PCIDevSetDWord in the device won't do it, that's expected. It will get rewritten. 

I don't think VirtualBox supplies any device with so many BARs so it's entirely possible that something isn't working. The trouble is that you have your code + ours, and we only have our code, so it's quite hard for us to debug the problem. 

One hint... what happens if you switch your VM to use EFI instead of the classic BIOS? I believe EFI should initialize all the PCI resources itself, so you might be able to see what happens even before an OS boots. 

And two more comments. I see that you have both the VirtualBox VGA device and your own. No one can tell you for certain that that won't cause problems. And you presumably want to use MSIs (otherwise you wouldn't bother with ICH9), but you're using quite old version of VirtualBox. There were several fixes in the MSI handling area in VirtualBox 5.0. 


----- Original Message ----- 
From: apallapothu at gmail.com 
To: klaus.espenlaub at oracle.com 
Cc: vbox-dev at virtualbox.org 
Sent: Tuesday, August 18, 2015 9:04:05 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna 
Subject: Re: [vbox-dev] ICH9 BAR5 access 

Hi Klaus, 

Thanks for the response. 

In the PCIe config space I set all BAR's to 0, using PCIDevSetDWord .... no address mapping from myside. 
I first register the region using PDMDevHlpPCIIORegionRegister with respective size. 
BAR0 = 0x800,0000 128 M 
BAR5 = 0x4,0000 256K 
Then I register memory call backs using PDMDevHlpMMIORegister for the size. 

While experimenting, I played with different base address in DevPciIch9.cpp "pGlobals->uPciBiosMmio = UINT32_C(0xB8000000);" which moved BAR's accordingly. 

While experimenting, I have tried setting start address for BAR's in PCIe config space, I saw that this address eventually gets overwritten by FakeBIOS and then OS. 

When I ran lspci on the guest I did not see conflict in address mapping. Attached lspci output. My pass through device shows up under VGA. 
I have added lspci output of fully functional PIIX3 chipset for comparison. 

At the end of the attachment, please note the VM debugger output in ICH9 chip set which apparently doesn't see the VGA device. 

Just to keep my message crisp, with the same device code, in PIIX3 I am able to see memory access to the addresses specified in BAR0, BAR5 while in ICH9, I only see access coming through in BAR0 and NOT BAR5. 


On Tue, Aug 18, 2015 at 2:25 PM, Klaus Espenlaub < klaus.espenlaub at oracle.com > wrote: 

Hi Ananth, 

On 18.08.2015 20:04, Ananth Pallapothu wrote: 

Hello Experts, 

I have added new pass through device to the VirtualBox setup . Registered all 6 BAR's with appropriate sizes, none exceeding 256M. All BAR's were set to reflect hardware functionality (assigned 0), eventually OS programmed base address regions with the sizes I have registered them with. Can you provide more details (how you map the regions initially and on remap)? Hard to say what's happening otherwise. 

My fundamental problem is, I have been able to access BAR0 and NOT BAR5. I tried playing with BIOSmmio address setting in DevPciIch9, that made difference in relocating BAR's but functionality remained the same (Not able to access BAR5) 

Interesting part is, PIIX3 chipset is fully functional ie., can access BAR5 in PIIX3 but NOT in ICH9. 
Could be that with PIIX3 there's no remap and with ICH9 there's a remap... really difficult to say anything with the sparse information. 


PS: There seems to be some problem with my email ID, so not sure whether my last email came through. Sorry if you have already received it. 


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