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** Changed in: qemu
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1837851
Title:
hv-tlbflush malfunctions on Intel host CPUs with neither EPT nor VPID
(qemu-kvm)
Status in QEMU:
Incomplete
Bug description:
Enabling hv-tlbflush on older hosts using Intel CPUs supporting VT-x
but neither EPT nor VPID will lead to bluescreens on the guest.
It seems KVM only checks if EPT is available, and if it isn't it
forcibly uses VPID. If that's *also* not available, it defaults to
basically a no-op hypercall, though windows is expecting the TLB to be
flushed.
hv-tlbflush is pretty useless on machines not supporting these
extensions anyway (only reasonably fix I can see would be to flush the
*entire* TLB on tlbflush hypercall in KVM (i.e. a kernel fix), but
that would remove any performance benefits), so I would suggest some
kind of preliminary check and warning/error if hv-tlbflush is
specified on such a host.
All CPUs mentioned in this thread[0] are confirmed to be affected by
the bug, and I have successfully reproduced it on an Intel Core2Duo
E8500.
[0] https://forum.proxmox.com/threads/windows-guest-bluescreen-with-
proxmox-6.56053/
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