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[PATCH v2 03/24] hw/xen: select kernel mode for per-vCPU event channel u
From: |
David Woodhouse |
Subject: |
[PATCH v2 03/24] hw/xen: select kernel mode for per-vCPU event channel upcall vector |
Date: |
Thu, 19 Oct 2023 16:39:59 +0100 |
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(+)
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);
--
2.40.1
- [PATCH v2 10/24] hw/xen: populate store frontend nodes with XenStore PFN/port, (continued)
- [PATCH v2 10/24] hw/xen: populate store frontend nodes with XenStore PFN/port, David Woodhouse, 2023/10/19
- [PATCH v2 01/24] i386/xen: Don't advertise XENFEAT_supervisor_mode_kernel, David Woodhouse, 2023/10/19
- [PATCH v2 20/24] hw/xenpv: fix '-nic' support for xen-net-device, David Woodhouse, 2023/10/19
- [PATCH v2 19/24] hw/i386/pc: support '-nic' for xen-net-device, David Woodhouse, 2023/10/19
- [PATCH v2 11/24] hw/xen: automatically assign device index to block devices, David Woodhouse, 2023/10/19
- [PATCH v2 15/24] hw/xen: add support for Xen primary console in emulated mode, David Woodhouse, 2023/10/19
- [PATCH v2 13/24] hw/xen: do not repeatedly try to create a failing backend device, David Woodhouse, 2023/10/19
- [PATCH v2 12/24] hw/xen: add get_frontend_path() method to XenDeviceClass, David Woodhouse, 2023/10/19
- [PATCH v2 07/24] hw/xen: Clean up event channel 'type_val' handling to use union, David Woodhouse, 2023/10/19
- [PATCH v2 03/24] hw/xen: select kernel mode for per-vCPU event channel upcall vector,
David Woodhouse <=
- [PATCH v2 04/24] hw/xen: don't clear map_track[] in xen_gnttab_reset(), David Woodhouse, 2023/10/19
- [PATCH v2 24/24] docs: update Xen-on-KVM documentation, David Woodhouse, 2023/10/19
- [PATCH v2 08/24] include: update Xen public headers to Xen 4.17.2 release, David Woodhouse, 2023/10/19
- [PATCH v2 16/24] hw/xen: handle soft reset for primary console, David Woodhouse, 2023/10/19