Patchwork KVM: PPC: Book3S HV: Fix bug causing loss of page dirty state

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Submitter Paul Mackerras
Date Nov. 20, 2012, 9:01 a.m.
Message ID <20121120090134.GD2994@bloggs.ozlabs.ibm.com>
Download mbox | patch
Permalink /patch/200264/
State New
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Comments

Paul Mackerras - Nov. 20, 2012, 9:01 a.m.
This fixes a bug where adding a new guest HPT entry via the H_ENTER
hcall would lose the "changed" bit in the reverse map information
for the guest physical page being mapped.  The result was that the
KVM_GET_DIRTY_LOG could return a zero bit for the page even though
the page had been modified by the guest.

This fixes it by only modifying the index and present bits in the
reverse map entry, thus preserving the reference and change bits.
We were also unnecessarily setting the reference bit, and this
fixes that too.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
This is against Alex Graf's kvm-ppc-next branch plus the series of three
patches I just sent, but it should be independent of that series.

 arch/powerpc/kvm/book3s_hv_rm_mmu.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
Alexander Graf - Nov. 20, 2012, 9:10 a.m.
On 20.11.2012, at 10:01, Paul Mackerras wrote:

> This fixes a bug where adding a new guest HPT entry via the H_ENTER
> hcall would lose the "changed" bit in the reverse map information
> for the guest physical page being mapped.  The result was that the
> KVM_GET_DIRTY_LOG could return a zero bit for the page even though
> the page had been modified by the guest.
> 
> This fixes it by only modifying the index and present bits in the
> reverse map entry, thus preserving the reference and change bits.
> We were also unnecessarily setting the reference bit, and this
> fixes that too.
> 
> Signed-off-by: Paul Mackerras <paulus@samba.org>

Thanks, applied to kvm-ppc-next.

Alex

> ---
> This is against Alex Graf's kvm-ppc-next branch plus the series of three
> patches I just sent, but it should be independent of that series.
> 
> arch/powerpc/kvm/book3s_hv_rm_mmu.c |    6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 2334000..fc3da32 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -59,10 +59,10 @@ void kvmppc_add_revmap_chain(struct kvm *kvm, struct revmap_entry *rev,
> 		head->back = pte_index;
> 	} else {
> 		rev->forw = rev->back = pte_index;
> -		i = pte_index;
> +		*rmap = (*rmap & ~KVMPPC_RMAP_INDEX) |
> +			pte_index | KVMPPC_RMAP_PRESENT;
> 	}
> -	smp_wmb();
> -	*rmap = i | KVMPPC_RMAP_REFERENCED | KVMPPC_RMAP_PRESENT; /* unlock */
> +	unlock_rmap(rmap);
> }
> EXPORT_SYMBOL_GPL(kvmppc_add_revmap_chain);
> 
> -- 
> 1.7.10.4
> 
> --
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Patch

diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 2334000..fc3da32 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -59,10 +59,10 @@  void kvmppc_add_revmap_chain(struct kvm *kvm, struct revmap_entry *rev,
 		head->back = pte_index;
 	} else {
 		rev->forw = rev->back = pte_index;
-		i = pte_index;
+		*rmap = (*rmap & ~KVMPPC_RMAP_INDEX) |
+			pte_index | KVMPPC_RMAP_PRESENT;
 	}
-	smp_wmb();
-	*rmap = i | KVMPPC_RMAP_REFERENCED | KVMPPC_RMAP_PRESENT; /* unlock */
+	unlock_rmap(rmap);
 }
 EXPORT_SYMBOL_GPL(kvmppc_add_revmap_chain);