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| author | David Woodhouse <dwmw@amazon.co.uk> | 2023-10-12 00:06:26 +0100 |
|---|---|---|
| committer | David Woodhouse <dwmw@amazon.co.uk> | 2023-11-06 10:03:45 +0000 |
| commit | 18e83f28bf39ffd2784aeb2e4e229096a86d349b (patch) | |
| tree | d68096ad48ca5dbfc01e1ecb03fcdbf5bcd91f4d /hw/i386/kvm | |
| parent | e7dbb62ff19ce55548c785d76e814e7b144e6217 (diff) | |
| download | qemu-18e83f28bf39ffd2784aeb2e4e229096a86d349b.zip qemu-18e83f28bf39ffd2784aeb2e4e229096a86d349b.tar.gz qemu-18e83f28bf39ffd2784aeb2e4e229096a86d349b.tar.bz2 | |
hw/xen: select kernel mode for per-vCPU event channel upcall vector
A guest which has configured the per-vCPU upcall vector may set the
HVM_PARAM_CALLBACK_IRQ param to fairly much anything other than zero.
For example, Linux v6.0+ after commit b1c3497e604 ("x86/xen: Add support
for HVMOP_set_evtchn_upcall_vector") will just do this after setting the
vector:
/* Trick toolstack to think we are enlightened. */
if (!cpu)
rc = xen_set_callback_via(1);
That's explicitly setting the delivery to GSI#1, but it's supposed to be
overridden by the per-vCPU vector setting. This mostly works in Qemu
*except* for the logic to enable the in-kernel handling of event channels,
which falsely determines that the kernel cannot accelerate GSI delivery
in this case.
Add a kvm_xen_has_vcpu_callback_vector() to report whether vCPU#0 has
the vector set, and use that in xen_evtchn_set_callback_param() to
enable the kernel acceleration features even when the param *appears*
to be set to target a GSI.
Preserve the Xen behaviour that when HVM_PARAM_CALLBACK_IRQ is set to
*zero* the event channel delivery is disabled completely. (Which is
what that bizarre guest behaviour is working round in the first place.)
Cc: qemu-stable@nongnu.org
Fixes: 91cce756179 ("hw/xen: Add xen_evtchn device for event channel emulation")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Diffstat (limited to 'hw/i386/kvm')
| -rw-r--r-- | hw/i386/kvm/xen_evtchn.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c index a731738..3d6f4b4 100644 --- a/hw/i386/kvm/xen_evtchn.c +++ b/hw/i386/kvm/xen_evtchn.c @@ -490,6 +490,12 @@ int xen_evtchn_set_callback_param(uint64_t param) break; } + /* If the guest has set a per-vCPU callback vector, prefer that. */ + if (gsi && kvm_xen_has_vcpu_callback_vector()) { + in_kernel = kvm_xen_has_cap(EVTCHN_SEND); + gsi = 0; + } + if (!ret) { /* If vector delivery was turned *off* then tell the kernel */ if ((s->callback_param >> CALLBACK_VIA_TYPE_SHIFT) == |