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

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Submitter Alexander Graf
Date May 30, 2014, 12:42 p.m.
Message ID <1401453776-55285-35-git-send-email-agraf@suse.de>
Download mbox | patch
Permalink /patch/354129/
State New
Headers show

Comments

Alexander Graf - May 30, 2014, 12:42 p.m.
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(-)

Patch

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;