[PULL 34/41] KVM: PPC: Book3S HV: Fix check for running inside guest in global_invalidates()

Alexander Graf
2014-05-30T12:43:06Z

From: Paul Mackerras <paulus@samba.org>

The global_invalidates() function contains a check that is intended
to tell whether we are currently executing in the context of a hypercall
issued by the guest. The reason is that the optimization of using a
local TLB invalidate instruction is only valid in that context. The
check was testing local_paca->kvm_hstate.kvm_vcore, which gets set
when entering the guest but no longer gets cleared when exiting the
guest. To fix this, we use the kvm_vcpu field instead, which does
get cleared when exiting the guest, by the kvmppc_release_hwthread()
calls inside kvmppc_run_core().

The effect of having the check wrong was that when kvmppc_do_h_remove()
got called from htab_write() on the destination machine during a
migration, it cleared the current cpu's bit in kvm->arch.need_tlb_flush.
This meant that when the guest started running in the destination VM,
it may miss out on doing a complete TLB flush, and therefore may end
up using stale TLB entries from a previous guest that used the same
LPID value.

This should make migration more reliable.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
---
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 1d6c56a..ac840c6 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -42,13 +42,14 @@ static int global_invalidates(struct kvm *kvm, unsigned long flags)

/*
* If there is only one vcore, and it's currently running,
+ * as indicated by local_paca->kvm_hstate.kvm_vcpu being set,
* we can use tlbiel as long as we mark all other physical
* cores as potentially having stale TLB entries for this lpid.
* If we're not using MMU notifiers, we never take pages away
* from the guest, so we can use tlbiel if requested.
* Otherwise, don't use tlbiel.
*/
- if (kvm->arch.online_vcores == 1 && local_paca->kvm_hstate.kvm_vcore)
+ if (kvm->arch.online_vcores == 1 && local_paca->kvm_hstate.kvm_vcpu)
global = 0;
else if (kvm->arch.using_mmu_notifiers)
global = 1;
--
1.8.1.4