On Mon, 2014-07-28 at 14:09 +0800, Liu Ping Fan wrote:
> In current code, the setup of hpte is under the risk of race with
> mmu_notifier_invalidate, i.e we may setup a hpte with a invalid pfn.
> Resolve this issue by sync the two actions by KVMPPC_RMAP_LOCK_BIT.
Please describe the race you think you see. I'm quite sure both Paul and
I went over that code and somewhat convinced ourselves that it was ok
but it's possible that we were both wrong :-)
Cheers,
Ben.
> Signed-off-by: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 8056107..e6dcff4 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -754,19 +754,24 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>
> if (hptep[0] & HPTE_V_VALID) {
> /* HPTE was previously valid, so we need to invalidate it */
> - unlock_rmap(rmap);
> hptep[0] |= HPTE_V_ABSENT;
> kvmppc_invalidate_hpte(kvm, hptep, index);
> /* don't lose previous R and C bits */
> r |= hptep[1] & (HPTE_R_R | HPTE_R_C);
> +
> + hptep[1] = r;
> + eieio();
> + hptep[0] = hpte[0];
> + asm volatile("ptesync" : : : "memory");
> + unlock_rmap(rmap);
> } else {
> + hptep[1] = r;
> + eieio();
> + hptep[0] = hpte[0];
> + asm volatile("ptesync" : : : "memory");
> kvmppc_add_revmap_chain(kvm, rev, rmap, index, 0);
> }
>
> - hptep[1] = r;
> - eieio();
> - hptep[0] = hpte[0];
> - asm volatile("ptesync" : : : "memory");
> preempt_enable();
> if (page && hpte_is_writable(r))
> SetPageDirty(page);
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