Re: [PATCH 2/2] kvm: ppc: booke: check range page invalidation progress on page setup

[Paolo Bonzini <pbonzini@redhat.com>]

Il 04/10/2013 15:38, Alexander Graf ha scritto:
> 
> On 07.08.2013, at 12:03, Bharat Bhushan wrote:
> 
>> When the MM code is invalidating a range of pages, it calls the KVM
>> kvm_mmu_notifier_invalidate_range_start() notifier function, which calls
>> kvm_unmap_hva_range(), which arranges to flush all the TLBs for guest pages.
>> However, the Linux PTEs for the range being flushed are still valid at
>> that point.  We are not supposed to establish any new references to pages
>> in the range until the ...range_end() notifier gets called.
>> The PPC-specific KVM code doesn't get any explicit notification of that;
>> instead, we are supposed to use mmu_notifier_retry() to test whether we
>> are or have been inside a range flush notifier pair while we have been
>> referencing a page.
>>
>> This patch calls the mmu_notifier_retry() while mapping the guest
>> page to ensure we are not referencing a page when in range invalidation.
>>
>> This call is inside a region locked with kvm->mmu_lock, which is the
>> same lock that is called by the KVM MMU notifier functions, thus
>> ensuring that no new notification can proceed while we are in the
>> locked region.
>>
>> Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
> 
> Acked-by: Alexander Graf <agraf@suse.de>
> 
> Gleb, Paolo, please queue for 3.12 directly.

Here is the backport.  The second hunk has a nontrivial conflict, so
someone please give their {Tested,Reviewed,Compiled}-by.

Paolo

diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c
index 1c6a9d7..c65593a 100644
--- a/arch/powerpc/kvm/e500_mmu_host.c
+++ b/arch/powerpc/kvm/e500_mmu_host.c
@@ -332,6 +332,13 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
 	unsigned long hva;
 	int pfnmap = 0;
 	int tsize = BOOK3E_PAGESZ_4K;
+	int ret = 0;
+	unsigned long mmu_seq;
+	struct kvm *kvm = vcpu_e500->vcpu.kvm;
+
+	/* used to check for invalidations in progress */
+	mmu_seq = kvm->mmu_notifier_seq;
+	smp_rmb();
 
 	/*
 	 * Translate guest physical to true physical, acquiring
@@ -449,6 +456,12 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
 		gvaddr &= ~((tsize_pages << PAGE_SHIFT) - 1);
 	}
 
+	spin_lock(&kvm->mmu_lock);
+	if (mmu_notifier_retry(kvm, mmu_seq)) {
+		ret = -EAGAIN;
+		goto out;
+	}
+
 	kvmppc_e500_ref_setup(ref, gtlbe, pfn);
 
 	kvmppc_e500_setup_stlbe(&vcpu_e500->vcpu, gtlbe, tsize,
@@ -457,10 +470,13 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
 	/* Clear i-cache for new pages */
 	kvmppc_mmu_flush_icache(pfn);
 
+out:
+	spin_unlock(&kvm->mmu_lock);
+
 	/* Drop refcount on page, so that mmu notifiers can clear it */
 	kvm_release_pfn_clean(pfn);
 
-	return 0;
+	return ret;
 }
 
 /* XXX only map the one-one case, for now use TLB0 */