Bug 203874

Summary: [patch] MSI/MSI-X interrupts don't work in VMware virtual machines
Product: Base System Reporter: bhavesh
Component: kernAssignee: freebsd-virtualization mailing list <virtualization>
Status: New ---    
Severity: Affects Many People CC: arunpereira, dmitry.wagin, heoj, igor, jhb, marius, ncrogers, pi, rgrimes
Priority: --- Keywords: patch
Version: CURRENT   
Hardware: amd64   
OS: Any   
Bug Depends on:    
Bug Blocks: 178795    
Description Flags
patch to remove VMware MSI/MSI-X quirk none

Description bhavesh 2015-10-19 16:32:06 UTC
Any PCI* device/driver that relies on MSI or MSI-X interrupts doesn't work in a VMware (ESXi hypervisor) virtual machine.

This is because of a quirk workaround that exists in the FreeBSD kernel that fails requests for MSI or MSI-X interrupt vectors when it detects that the PCIe Root Port or PCI bridge device is a VMware device (PCI Vendor ID 15adh, Device ID 0790h or 07a0h)

The comment in the code suggests MSI/MSI-X didn't work in older versions of ESXi:

         * MSI-X allocation doesn't work properly for devices passed through
         * by VMware up to at least ESXi 5.1.

I don't think this is true any more. Verified this by booting with:


in /boot/loader.conf

Everything seems to be working fine with various devices and drivers (passthrough ixgbe/ixgbevf, vmxnet3, etc.) with this boot workaround in a FreeBSD 10.2 VM on ESXi 6.0.

I'll propose a trivial patch to remove this quirk workaround.
Comment 1 bhavesh 2015-10-19 16:39:04 UTC
Created attachment 162212 [details]
patch to remove VMware MSI/MSI-X quirk
Comment 2 Marius Strobl freebsd_committer 2015-10-20 21:53:36 UTC
Removing the ESXi MSI-X quirk altogether simply is way too gross as the intention is to provide a setup which at least works out of the box, also on older versions of the the VMM and even if that doesn't yield the optimal configuration. As you apparently work for VMware, could you please get the revision ID in the PCI header of 0x079015ad and 0x07a015ad bridges bumped for the implementations that have MSI-X allocation fixed - if that hasn't already be done, yet -, so we can distinguish the good from the bad ones in the PCI code? My logs indicate that at least the bridges reporting revision 0x1 were affected.
Comment 3 bhavesh 2015-10-20 22:28:45 UTC
(In reply to Marius Strobl from comment #2)

I tried to search for the history behind why this quirk was introduced for VMware virtual machines in the first place, as we've never shipped a version of ESXi where the implementation of MSI or MSI-X was broken, like the comment suggests it was in ESXi 5.1 and before.

So there have been no bumps to the PCI revision IDs of these devices that can identify when it was broken v/s fixed as from our POV it was never broken.

Can you point me to some bug report or mailing list archive or something that details what was supposedly broken w.r.t. "MSI-X allocation on ESXi?"
Comment 4 Marius Strobl freebsd_committer 2015-10-25 18:06:01 UTC
(In reply to bhavesh from comment #3)

The problem with broken versions of ESXi is that allocation of MSI-X vectors fails when tried for the first time but succeeds on subsequent attempts. As Jack Vogel from Intel pointed out, this behavior inherently reminds of a design bug in Linux/KVM:
The full thread starts here:
I think at that time igb(4) additionally had an orthogonal and meanwhile fixed bug, causing it to fail to properly fall back to MSI or even INTx, leading to an overall non-working default setup when run under ESXi back then.

Apart from that, there was a private and independent report to jhb@freebsd.org and me in June 2013, indicating that using INTx with ESXi 5.1 causes interrupt storms on the FreeBSD side. In addition to the VMware documentation of that time listing only three devices known-working with MSI-X in pass-through mode, this lead to the conclusion that MSIs are the only thing that reliably works with ESXi. Consequently, the current behavior of blacklisting the VMware PCI bridges for MSI-X (but contrary to your claim, not for MSI) was implemented and verified to yield a configuration which works out-of-the-box in the known problematic setups involving ESXi.

As for the MSI-X allocation bug, it likely isn't/wasn't present in the bridge code of ESXi itself but rather in its LAPIC emulation. Still, bumping the PCI revision IDs to indicate ESXi versions where that problem has been fixed would be way preferable to having to query the hypervisor version by other means in the machine-independant PCI code of FreeBSD for limiting the blacklist entries for VMware.
Comment 5 bhavesh 2015-10-26 18:26:40 UTC
(In reply to Marius Strobl from comment #4)

Thanks for the additional background. I had not found those in my searching.

It seems https://lists.freebsd.org/pipermail/freebsd-stable/2012-October/070220.html is being used as the authoritative reasoning behind blacklisting VMware VMs (via the PCI bridge and PCIe root port VID/DID) for lack of MSI-X support.

Unfortunately that e-mail/thread doesn't give more details than:

When my driver would first attempt to get some vectors the Linux code would go look at the vector table, but the way the PCI code in FreeBSD works that table is not set up yet, so Linux would see no legitimate vectors in the table, and decide the guest was ineligible for MSIX :(, but by this time the FreeBSD code actually DID write some vectors into the table, and thus when you load the driver the SECOND time Linux would see the table populated and TADA!! would enable the guest to use MSIX.

Now, I went thru a bunch of efforts via our Linux team here to have the KVM
code fixed, its design was bogus, and I believe it has been, but it sounds like maybe
VMWare has the same broken design??

Need more details, like why the author of that e-mail believes "its design was bogus" and can he mention the GIT commit or a link to the discussion where it was supposedly "fixed" in KVM?

I'm Cc'ing Jack directly. Hopefully the e-mail address is still valid.

Comment 6 igor 2017-03-28 12:44:05 UTC
(In reply to bhavesh from comment #5)

Is there still a good idea on to keep this blacklisting for ESXi, other than exposing bugs in fall-back code in drivers (https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=218113)?

It's been nearly a year and a half since the last comment?

I've removed the blacklisting for 11-RELEASE on my box inside ESXi 6.5 and there doesn't seem to be any previously reported signs of "badness" with LSI SAS emulation and igb(4) passthrough so far.
Comment 7 Rodney W. Grimes freebsd_committer 2017-05-31 19:18:37 UTC
This needs to be regression tested as far back as ESXi 5.0 imho, as that is still a common production environment.

It would be nice to have a fix that just did the right thing on any of ESXi 5.0 to 6.5.

It would also be nice to have a fix that works on FreeBSD 10, 11 and -current, and even nicer if that fix could back port even further back.
Comment 8 igor 2017-05-31 19:29:42 UTC
(In reply to Rodney W. Grimes from comment #7)

ESXi 5.0 and 5.1 had their general support discontinued on 24th August 2016: https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2145103

Do you have any empirical evidence to suggest that 5.0 is "is still a common production environment," or is this more of a "Windows XP"-style "let's just use it in a hope it doesn't break" type of thing? Further, as bhavesh@vmware.com  pointed out ESXi was never broken, and there is hardly anything but speculative rumours to support the original inclusion (not even a reproducible bug report!)
Comment 9 Marius Strobl freebsd_committer 2017-05-31 19:39:00 UTC
One thing that came to my mind regarding some people apparently not being able to reproduce the original problem is that it may also depend on the virtualization capabilities of the hardware used, e. g. APICv, AVIC, MSI/MSI-X remapping etc., i. e. the bug may be present in the full software emulation of ESXi (or some versions thereof) but hidden when interrupt handling is assisted by hardware.
Comment 10 igor 2017-05-31 19:44:07 UTC
(In reply to Marius Strobl from comment #9)

And without any bug reports that lead to the exclusion of MSI-X support under FreeBSD we'll never know. Linux has MSI-X under ESXi, if I recall correctly, so chances are that it's a "FreeBSD problem" not an ESXi one.
Comment 11 Jin Heo 2017-07-24 22:14:53 UTC

This bug has been around quite a while. Is there anything that VMware needs to do to resolve this issue?

Comment 12 John Baldwin freebsd_committer freebsd_triage 2018-11-15 18:32:08 UTC
Hmm, I don't recall which issue we ran into with VMWare.  We have had some issues with Xen hypervisors that might be related.  They had to do with how the hypervisor cached MSI-X table entries and that it didn't notice updates to the table that FreeBSD's kernel performed because it assumed the table was not modified once MSI-X was enabled in the capability register.

Commits related to those issues are r302181 + r302635 and r310806.

From the thread about igb(4) that was quoted, it sounds like it might be a similar issue where VMWare might be assuming that MSI-X tables are only updated in a particular order.  FreeBSD follows a scheme where it marks all the table entries as disabled and then enables MSI-X in the capability register and then writes individual table entries as the driver calls bus_setup_intr().  This means that the table can change while MSI-X is enabled.  A table entry might also be written multiple times if a device driver moves an interrupt to a different CPU than the one chosen by the system.  In real hardware this works fine as the hardware checks the table to compose the MSI message before sending each message.  Hypervisors might choose to cache the table since reading the actual table might be too expensive.  However, in that case hypervisors have to trap all writes to the table and update their cached copy for each write.  The Xen issues had to do with Xen assuming it could ignore writes made while MSI-X was active since Linux writes the whole table and then enables MSI-X.  I would start by seeing if you have a shadow copy of the MSI-X table and if you make assumptions about which writes to that table have to be trapped to update the shadow table.
Comment 13 Rodney W. Grimes freebsd_committer 2019-01-04 16:15:18 UTC
This is a ping, we need to move forward on this issue.
Comment 14 igor 2019-01-04 17:58:53 UTC
(In reply to Rodney W. Grimes from comment #13)

Given that (a) there is absolutely no definitive background as to why the hack, pardon me, "quirk" was inserted in in the first place, (b) utter disinterest in getting to the bottom of the hack from the kernel "folk," and (c) existence of viable alternatives, we can safely say that the hack these patches were trying to revert was a tombstone on FreeBSD as a passthrough guest---I, for one, just like in bug #178795, have moved onto Linux when I need passthrough; and I doubt we were the only two.

Now, given that I do like FreeBSD, I am quite happy to spin up an ESXi box and try whatever.

Incidentally, comment #12 doesn't explain why de-quirking worked fine, or why Linux/Windows guests are unaffected.
Comment 15 John Baldwin freebsd_committer freebsd_triage 2019-01-04 18:41:27 UTC
(In reply to igor from comment #14)
Comment #12 explains why another hypervisor had issues with FreeBSD due to an incomplete emulation of MSI-X.  However, the questions it raises can only be answered by someone who knows how VMWare's hypervisor implements passthrough and how it has changed over time.  For example, on Xen we employ a workaround for the known-broken versions (and Xen has been fixed).  It may be that if VMWare had a similar issue it was previously fixed as well which would explain why the quirk may not be needed on newer versions of VMWare, but someone from VMWare would have to answer that question.
Comment 16 igor 2019-01-04 19:16:31 UTC
(In reply to John Baldwin from comment #15)

The reply from VMWare is in comment #3---their implementation was never broken. They also asked for specific bug reports to be identified where the buggy behaviour can be observed; yet, none were provided, and that was back in 2015!

Given that there doesn't seem to be a problem with MSI-X on Linux guests nor Windows guests, what does the application of Occam's razor yield?.. As for VMWare, how would anyone even begin to investigate an unexpected behaviour when that behaviour is only described as "doesn't work in some non-specific circumstances"?
Comment 17 John Baldwin freebsd_committer freebsd_triage 2019-01-04 19:32:09 UTC
I don't think the commenter in #3 understood what "broken" might mean in the context of MSI or MSI-X, so I attempted to give more detail on how a particular type of breakage might boot Linux ok but not FreeBSD (as was the case for Xen).  However, if VMWare 6.0 is known to work we could alter the quirk to instead use the version of VMWare (e.g. via SMBIOS strings or what not) instead of PCI device IDs to know when to apply the quirk.

In terms of what VMware would investigate, I gave very specific details (do you implement an MSI-X shadow table, etc.) that someone familiar with the implementation would be able to investigate.  This is not "not caring", this is "the best suggestions I can give of what to look for given what I know of how FreeBSD's use of MSI-X differs from Linux assuming I don't get to look at the sources myself".
Comment 18 igor 2019-01-04 19:42:39 UTC
(In reply to John Baldwin from comment #17)

In order to investigate anything that sporadically breaks, you need to know how to break it. Like I said in comment #6 when I disabled the hack, nothing was breaking; so why would anyone spend $$$ investigating anything without even a clue as to a path to break it? My interpretation of comment #3 is "Our implementation is in accordance with the spec. Do you have a specific scenario that takes our implementation outside of the spec?" To which nothing was produced.

Similarly, as bug #218113 shows MSI-X was also "hacked" for KVM (I don't know if that's still the case), so it would seem that according to FreeBSD neither KVM nor ESXi implement the hardware side of MSI-X properly? C'mon! :-)
Comment 19 Dmitry Wagin 2019-05-29 18:37:58 UTC
WMware ESXi 5.5.0, 3248547 + IBM System x3550 M3 2xIntel Xeon X5670
MSI-X not working, with hw.pci.honor_msi_blacklist=0 - rebooting.
Comment 20 Arun Pereira 2019-07-30 02:04:08 UTC
In the case of VMware 5.5, it's VMware vmx binary that's crashing. It doesn't crash on VMware 6.7. However, please note that VMware 5.5 is unsupported and hence you'd be expected to use 6.7.