** Description changed:
+ [Impact]
+ On CPUs with no EPT support, or when disabling kvm-intel ept support by use
of ept=0 module parameter, users are not able to launch a linux VM.
+
+ [Test case]
+ # modprobe kvm-intel ept=0
+ # cat /sys/module/kvm_intel/parameters/ept
+ N
+ # qemu-system-x86_64 -enable-kvm -kernel /boot/vmlinuz-4.15.0-68-generic
+
+ Make sure you get console log at all. With the bug, there is not a
+ single line of output.
+
+ [Regression potential]
+ The fix might cause some very specific use of virtualization to fail, but no
pratical case is known.
+
+ ===============================
+
Mostly the same info as on a related kernel.org bugzilla entr[0].
[0]: https://bugzilla.kernel.org/show_bug.cgi?id=205441
We got issues reported with old Intel CPUs and Linux guest run with
QEMU/KVM after a recent kernel update which is based on
Ubuntu-5.0.0-33.35.
I bisected this here, with following result:
- git bisect log
+ git bisect log
# bad: [3b931173c97b0d73f80ea55b72bb2966a246167f] UBUNTU: Ubuntu-5.0.0-33.35
# good: [5d5a6b36e94909962297fae609bff487de3cc43a] UBUNTU: Ubuntu-5.0.0-30.32
git bisect start '3b931173c97b0d73f80ea55b72bb2966a246167f'
'5d5a6b36e94909962297fae609bff487de3cc43a'
# good: [7b4f844b33969ab166800f8936beef153fab736e] net/ibmvnic: free reset
work
of removed device from queue
git bisect good 7b4f844b33969ab166800f8936beef153fab736e
# bad: [6c1fc88702a4f33886b44ce5b6f374893b95e369] arm64: tlb: Ensure we
execute
an ISB following walk cache invalidation
git bisect bad 6c1fc88702a4f33886b44ce5b6f374893b95e369
# good: [e627a027b54eccc95f9e374d69aead7f1498877b] loop: Add
LOOP_SET_DIRECT_IO
to compat ioctl
git bisect good e627a027b54eccc95f9e374d69aead7f1498877b
# good: [29919eff6333bc67ec580b454afdd8b49883df2f] libata/ahci: Drop PCS quirk
for Denverton and beyond
git bisect good 29919eff6333bc67ec580b454afdd8b49883df2f
# good: [cb44193f94af73928f8df049ffbb6b4a0be136ae] PM / devfreq: passive: fix
compiler warning
git bisect good cb44193f94af73928f8df049ffbb6b4a0be136ae
# good: [b1d479b27b26966aea931094b31864979d7f8102] scsi: implement .cleanup_rq
callback
git bisect good b1d479b27b26966aea931094b31864979d7f8102
# bad: [ec15813844b05d8cbd4352c65a20e57d16f9f936] media: sn9c20x: Add MSI
MS-1039 laptop to flip_dmi_table
git bisect bad ec15813844b05d8cbd4352c65a20e57d16f9f936
# good: [e83601f51a90d9739ced9ff42b6f202f8f802c72] parisc: Disable HP HSC-PCI
Cards to prevent kernel crash
git bisect good e83601f51a90d9739ced9ff42b6f202f8f802c72
# good: [6d393bdf3b3f4b629070329488d3c6a3e142602b] KVM: x86: set
ctxt->have_exception in x86_decode_insn()
git bisect good 6d393bdf3b3f4b629070329488d3c6a3e142602b
# bad: [208007519a7385a57b0c0a3c180142a521594876] KVM: x86: Manually calculate
reserved bits when loading PDPTRS
git bisect bad 208007519a7385a57b0c0a3c180142a521594876
# first bad commit: [208007519a7385a57b0c0a3c180142a521594876] KVM: x86:
Manually calculate reserved bits when loading PDPTRS
Which is:
- KVM: x86: Manually calculate reserved bits when loading PDPTRS
+ KVM: x86: Manually calculate reserved bits when loading PDPTRS
- BugLink: https://bugs.launchpad.net/bugs/1848367
+ BugLink: https://bugs.launchpad.net/bugs/1848367
- commit 16cfacc8085782dab8e365979356ce1ca87fd6cc upstream.
+ commit 16cfacc8085782dab8e365979356ce1ca87fd6cc upstream.
- Manually generate the PDPTR reserved bit mask when explicitly loading
- PDPTRs. The reserved bits that are being tracked by the MMU reflect the
- current paging mode, which is unlikely to be PAE paging in the vast
- majority of flows that use load_pdptrs(), e.g. CR0 and CR4 emulation,
- __set_sregs(), etc... This can cause KVM to incorrectly signal a bad
- PDPTR, or more likely, miss a reserved bit check and subsequently fail
- a VM-Enter due to a bad VMCS.GUEST_PDPTR.
+ Manually generate the PDPTR reserved bit mask when explicitly loading
+ PDPTRs. The reserved bits that are being tracked by the MMU reflect the
+ current paging mode, which is unlikely to be PAE paging in the vast
+ majority of flows that use load_pdptrs(), e.g. CR0 and CR4 emulation,
+ __set_sregs(), etc... This can cause KVM to incorrectly signal a bad
+ PDPTR, or more likely, miss a reserved bit check and subsequently fail
+ a VM-Enter due to a bad VMCS.GUEST_PDPTR.
- Add a one off helper to generate the reserved bits instead of sharing
- code across the MMU's calculations and the PDPTR emulation. The PDPTR
- reserved bits are basically set in stone, and pushing a helper into
- the MMU's calculation adds unnecessary complexity without improving
- readability.
+ Add a one off helper to generate the reserved bits instead of sharing
+ code across the MMU's calculations and the PDPTR emulation. The PDPTR
+ reserved bits are basically set in stone, and pushing a helper into
+ the MMU's calculation adds unnecessary complexity without improving
+ readability.
- Oppurtunistically fix/update the comment for load_pdptrs().
+ Oppurtunistically fix/update the comment for load_pdptrs().
- Note, the buggy commit also introduced a deliberate functional change,
- "Also remove bit 5-6 from rsvd_bits_mask per latest SDM.", which was
- effectively (and correctly) reverted by commit cd9ae5fe47df ("KVM: x86:
- Fix page-tables reserved bits"). A bit of SDM archaeology shows that
- the SDM from late 2008 had a bug (likely a copy+paste error) where it
- listed bits 6:5 as AVL and A for PDPTEs used for 4k entries but reserved
- for 2mb entries. I.e. the SDM contradicted itself, and bits 6:5 are and
- always have been reserved.
+ Note, the buggy commit also introduced a deliberate functional change,
+ "Also remove bit 5-6 from rsvd_bits_mask per latest SDM.", which was
+ effectively (and correctly) reverted by commit cd9ae5fe47df ("KVM: x86:
+ Fix page-tables reserved bits"). A bit of SDM archaeology shows that
+ the SDM from late 2008 had a bug (likely a copy+paste error) where it
+ listed bits 6:5 as AVL and A for PDPTEs used for 4k entries but reserved
+ for 2mb entries. I.e. the SDM contradicted itself, and bits 6:5 are and
+ always have been reserved.
- Fixes: 20c466b56168d ("KVM: Use rsvd_bits_mask in load_pdptrs()")
- Cc: [email protected]
- Cc: Nadav Amit <[email protected]>
- Reported-by: Doug Reiland <[email protected]>
- Signed-off-by: Sean Christopherson <[email protected]>
- Reviewed-by: Peter Xu <[email protected]>
- Signed-off-by: Paolo Bonzini <[email protected]>
- Signed-off-by: Greg Kroah-Hartman <[email protected]>
- Signed-off-by: Kamal Mostafa <[email protected]>
- Signed-off-by: Kleber Sacilotto de Souza <[email protected]>
+ Fixes: 20c466b56168d ("KVM: Use rsvd_bits_mask in load_pdptrs()")
+ Cc: [email protected]
+ Cc: Nadav Amit <[email protected]>
+ Reported-by: Doug Reiland <[email protected]>
+ Signed-off-by: Sean Christopherson <[email protected]>
+ Reviewed-by: Peter Xu <[email protected]>
+ Signed-off-by: Paolo Bonzini <[email protected]>
+ Signed-off-by: Greg Kroah-Hartman <[email protected]>
+ Signed-off-by: Kamal Mostafa <[email protected]>
+ Signed-off-by: Kleber Sacilotto de Souza <[email protected]>
-
- This one is also included in the 4.19.81 (or more correctly, it's there since
+ This one is also included in the 4.19.81 (or more correctly, it's there since
v4.19.77) with commit 496cf984a60edb5534118a596613cc9971e406e8 [0] or
upstream commit 16cfacc8085782dab8e365979356ce1ca87fd6cc [1].
[0]:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit/?h=v4.19.82&id=496cf984a60edb5534118a596613cc9971e406e8
[1]:
https://git.kernel.org/torvalds/c/16cfacc8085782dab8e365979356ce1ca87fd6cc
Funny thing is: I cannot reproduce this with a 5.3.7 (Eoan) kernel, which
_also_
includes above commit. So possible another patch is missing in the backport,
did not find anything obvious though...
So summary for reproducer:
* dust of an host with old Intel CPU, e.g.: Intel Core2Duo CPU E8500 @3.16GHz
- (something else westmer, conroe or the like should work too, or if it's
+ (something else westmer, conroe or the like should work too, or if it's
released
- over 10 years ago.
+ over 10 years ago.
* Install a Linux Distro or just boot the installer of that in a VM, I used
Debian 9,
- as our users had issues with that but *not* with an ubuntu 19.10 VM.
+ as our users had issues with that but *not* with an ubuntu 19.10 VM.
* see how it boot loops once a stable-kernel with above[0] backported
- is used on the host
+ is used on the host
** Changed in: linux (Ubuntu Disco)
Status: New => In Progress
** Changed in: linux (Ubuntu Bionic)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1851709
Title:
Ubuntu-5.0.0-33.35 introduces KVM regression with old Intel CPUs and
Linux guests
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