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KVM: x86/xen: remove WARN_ON_ONCE() with false positives in evtchn delivery

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The kvm_xen_inject_vcpu_vector() function has a comment saying "the fast
version will always work for physical unicast", justifying its use of
kvm_irq_delivery_to_apic_fast() and the WARN_ON_ONCE() when that fails.

In fact that assumption isn't true if X2APIC isn't in use by the guest
and there is (8-bit x)APIC ID aliasing. A single "unicast" destination
APIC ID *may* then be delivered to multiple vCPUs. Remove the warning,
and in fact it might as well just call kvm_irq_delivery_to_apic().

Reported-by: Michal Luczaj <mhal@rbox.co>
Fixes: fde0451be8 ("KVM: x86/xen: Support per-vCPU event channel upcall via local APIC")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20240227115648.3104-4-dwmw2@infradead.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
David Woodhouse
2024-02-27 11:49:17 +00:00
committed by Sean Christopherson
parent 8e62bf2bfa
commit 66e3cf729b
1 changed files with 2 additions and 4 deletions
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6
arch/x86/kvm/xen.c
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@@ -10,7 +10,7 @@
#include "x86.h"
#include "xen.h"
#include "hyperv.h"
#include "lapic.h"
#include "irq.h"
#include <linux/eventfd.h>
#include <linux/kvm_host.h>
@@ -570,7 +570,6 @@ void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)
void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
{
struct kvm_lapic_irq irq = { };
int r;
irq.dest_id = v->vcpu_id;
irq.vector = v->arch.xen.upcall_vector;
@@ -579,8 +578,7 @@ void kvm_xen_inject_vcpu_vector(struct kvm_vcpu *v)
irq.delivery_mode = APIC_DM_FIXED;
irq.level = 1;
/* The fast version will always work for physical unicast */
WARN_ON_ONCE(!kvm_irq_delivery_to_apic_fast(v->kvm, NULL, &irq, &r, NULL));
kvm_irq_delivery_to_apic(v->kvm, NULL, &irq, NULL);
}
/*