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Subject[PATCH v4 08/13] KVM: xen: prevent vcpu_id from changing whilst shared_info is valid
Date
From: Paul Durrant <pdurrant@amazon.com>

To further prepare for automatically using the vcpu_info structures
embedded in the shared_info page, we need to ensure that the Xen vcpu_id
cannot change under our feet. We can do this by simply returning -EBUSY
to any attempt to modify the attribute while the shinfo_cache is active.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
---
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org

v3:
- New in this version.
---
Documentation/virt/kvm/api.rst | 3 ++-
arch/x86/kvm/xen.c | 18 ++++++++++++++----
2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index e9df4df6fe48..8d85fd7709f0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5605,7 +5605,8 @@ KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID
This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates
support for KVM_XEN_HVM_CONFIG_EVTCHN_SEND features. It sets the Xen
vCPU ID of the given vCPU, to allow timer-related VCPU operations to
- be intercepted by KVM.
+ be intercepted by KVM. Note that this must be set before the
+ shared_info page is set.

KVM_XEN_VCPU_ATTR_TYPE_TIMER
This attribute is available when the KVM_CAP_XEN_HVM ioctl indicates
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 9449cfe1048f..a9aada47e9b8 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -752,6 +752,18 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
return r;
}

+static int kvm_xen_set_vcpu_id(struct kvm_vcpu *vcpu, unsigned int vcpu_id)
+{
+ struct kvm *kvm = vcpu->kvm;
+ struct gfn_to_pfn_cache *gpc = &kvm->arch.xen.shinfo_cache;
+
+ if (gpc->active)
+ return -EBUSY;
+
+ vcpu->arch.xen.vcpu_id = vcpu_id;
+ return 0;
+}
+
int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
{
int idx, r = -ENOENT;
@@ -941,10 +953,8 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
case KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID:
if (data->u.vcpu_id >= KVM_MAX_VCPUS)
r = -EINVAL;
- else {
- vcpu->arch.xen.vcpu_id = data->u.vcpu_id;
- r = 0;
- }
+ else
+ r = kvm_xen_set_vcpu_id(vcpu, data->u.vcpu_id);
break;

case KVM_XEN_VCPU_ATTR_TYPE_TIMER:
--
2.39.2
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