| Message ID | 20231019154020.99080-4-dwmw2@infradead.org |
|---|---|
| State | New |
| Headers | show |
| Series | Get Xen PV shim running in Qemu, add net & console | expand |
On 19/10/2023 16:39, David Woodhouse wrote: > From: David Woodhouse <dwmw@amazon.co.uk> > > 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.) > > Fixes: 91cce756179 ("hw/xen: Add xen_evtchn device for event channel emulation") > Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> > --- > hw/i386/kvm/xen_evtchn.c | 6 ++++++ > include/sysemu/kvm_xen.h | 1 + > target/i386/kvm/xen-emu.c | 7 +++++++ > 3 files changed, 14 insertions(+) > Reviewed-by: Paul Durrant <paul@xen.org>
diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c index a731738411..3d6f4b4a0a 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) == diff --git a/include/sysemu/kvm_xen.h b/include/sysemu/kvm_xen.h index 595abfbe40..961c702c4e 100644 --- a/include/sysemu/kvm_xen.h +++ b/include/sysemu/kvm_xen.h @@ -22,6 +22,7 @@ int kvm_xen_soft_reset(void); uint32_t kvm_xen_get_caps(void); void *kvm_xen_get_vcpu_info_hva(uint32_t vcpu_id); +bool kvm_xen_has_vcpu_callback_vector(void); void kvm_xen_inject_vcpu_callback_vector(uint32_t vcpu_id, int type); void kvm_xen_set_callback_asserted(void); int kvm_xen_set_vcpu_virq(uint32_t vcpu_id, uint16_t virq, uint16_t port); diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c index 619240398a..3ba636b09a 100644 --- a/target/i386/kvm/xen-emu.c +++ b/target/i386/kvm/xen-emu.c @@ -424,6 +424,13 @@ void kvm_xen_set_callback_asserted(void) } } +bool kvm_xen_has_vcpu_callback_vector(void) +{ + CPUState *cs = qemu_get_cpu(0); + + return cs && !!X86_CPU(cs)->env.xen_vcpu_callback_vector; +} + void kvm_xen_inject_vcpu_callback_vector(uint32_t vcpu_id, int type) { CPUState *cs = qemu_get_cpu(vcpu_id);