Commit 24c16637 authored by Sean Christopherson's avatar Sean Christopherson
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KVM: x86: Don't bleed PVCLOCK_GUEST_STOPPED across PV clocks 



When updating a specific PV clock, make a full copy of KVM's reference
copy/cache so that PVCLOCK_GUEST_STOPPED doesn't bleed across clocks.
E.g. in the unlikely scenario the guest has enabled both kvmclock and Xen
PV clock, a dangling GUEST_STOPPED in kvmclock would bleed into Xen PV
clock.

Using a local copy of the pvclock structure also sets the stage for
eliminating the per-vCPU copy/cache (only the TSC frequency information
actually "needs" to be cached/persisted).

Fixes: aa096aa0 ("KVM: x86/xen: setup pvclock updates")
Reviewed-by: default avatarPaul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/20250201013827.680235-7-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent ca28aa63

arch/x86/kvm/x86.c

+8 −5
Original line number Diff line number Diff line
@@ -3123,8 +3123,11 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v, 
{

	struct kvm_vcpu_arch *vcpu = &v->arch;

	struct pvclock_vcpu_time_info *guest_hv_clock;

	struct pvclock_vcpu_time_info hv_clock;

	unsigned long flags;



	memcpy(&hv_clock, &vcpu->hv_clock, sizeof(hv_clock));



	read_lock_irqsave(&gpc->lock, flags);

	while (!kvm_gpc_check(gpc, offset + sizeof(*guest_hv_clock))) {

		read_unlock_irqrestore(&gpc->lock, flags);
@@ -3144,25 +3147,25 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v, 
	 * it is consistent.

	 */



	guest_hv_clock->version = vcpu->hv_clock.version = (guest_hv_clock->version + 1) | 1;

	guest_hv_clock->version = hv_clock.version = (guest_hv_clock->version + 1) | 1;

	smp_wmb();



	/* retain PVCLOCK_GUEST_STOPPED if set in guest copy */

	vcpu->hv_clock.flags |= (guest_hv_clock->flags & PVCLOCK_GUEST_STOPPED);

	hv_clock.flags |= (guest_hv_clock->flags & PVCLOCK_GUEST_STOPPED);



	memcpy(guest_hv_clock, &vcpu->hv_clock, sizeof(*guest_hv_clock));

	memcpy(guest_hv_clock, &hv_clock, sizeof(*guest_hv_clock));



	if (force_tsc_unstable)

		guest_hv_clock->flags &= ~PVCLOCK_TSC_STABLE_BIT;



	smp_wmb();



	guest_hv_clock->version = ++vcpu->hv_clock.version;

	guest_hv_clock->version = ++hv_clock.version;



	kvm_gpc_mark_dirty_in_slot(gpc);

	read_unlock_irqrestore(&gpc->lock, flags);



	trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);

	trace_kvm_pvclock_update(v->vcpu_id, &hv_clock);

}



static int kvm_guest_time_update(struct kvm_vcpu *v)