On 07/04/21 19:40, Marcelo Tosatti wrote:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe806e894212..0a83eff40b43 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2562,10 +2562,12 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
kvm_hv_invalidate_tsc_page(kvm);
- spin_lock(&ka->pvclock_gtod_sync_lock);
kvm_make_mclock_inprogress_request(kvm);
+
Might be good to serialize against two kvm_gen_update_masterclock
callers? Otherwise one caller could clear KVM_REQ_MCLOCK_INPROGRESS,
while the other is still at pvclock_update_vm_gtod_copy().
Makes sense, but this stuff has always seemed unnecessarily complicated
to me.
KVM_REQ_MCLOCK_INPROGRESS is only needed to kick running vCPUs out of
the execution loop; clearing it in kvm_gen_update_masterclock is
unnecessary, because KVM_REQ_CLOCK_UPDATE takes pvclock_gtod_sync_lock
too and thus will already wait for pvclock_update_vm_gtod_copy to end.
I think it's possible to use a seqcount in KVM_REQ_CLOCK_UPDATE instead
of KVM_REQ_MCLOCK_INPROGRESS. Both cause the vCPUs to spin. I'll take a
look.
Paolo
