On 18/01/2025 00:55, Sean Christopherson wrote:
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.
... but the line I queried in the previous patch squashes the flag
before the Xen PV clock is set up, so no bleed?
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: aa096aa0a05f ("KVM: x86/xen: setup pvclock updates")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3c4d210e8a9e..5f3ad13a8ac7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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)
