On 29.02.20 21:17, Jim Mattson wrote:
Since UMIP emulation is broken, I'm not sure why anyone would use it.
(Sorry, Paolo.)
FWIW, adding "-umip" to the "-cpu host" in my qemu setup works around
the bug.
Jan
On Sat, Feb 29, 2020 at 11:21 AM Jan Kiszka <jan.kiszka@xxxxxx> wrote:
On 29.02.20 20:00, Jim Mattson wrote:
On Sat, Feb 29, 2020 at 10:33 AM Oliver Upton <oupton@xxxxxxxxxx> wrote:
Hi Jan,
On Sat, Feb 29, 2020 at 10:00 AM Jan Kiszka <jan.kiszka@xxxxxx> wrote:
Is this expected to cause regressions on less common workloads?
Jailhouse as L1 now fails when Linux as L2 tries to boot a CPU: L2-Linux
gets a triple fault on load_current_idt() in start_secondary(). Only
bisected so far, didn't debug further.
I'm guessing that Jailhouse doesn't use 'descriptor table exiting', so
when KVM gets the corresponding exit from L2 the emulation burden is
on L0. We now refuse the emulation, which kicks a #UD back to L2. I
can get a patch out quickly to address this case (like the PIO exiting
one that came in this series) but the eventual solution is to map
emulator intercept checks into VM-exits + call into the
nested_vmx_exit_reflected() plumbing.
If Jailhouse doesn't use descriptor table exiting, why is L0
intercepting descriptor table instructions? Is this just so that L0
can partially emulate UMIP on hardware that doesn't support it?
That seems to be the case: My host lacks umip, L1 has it. So, KVM is
intercepting descriptor table load instructions to emulate umip.
Jailhouse never activates that interception.
Jan
