Hope I am right. Take the following seq as an example
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);
} else {
kvmppc_add_revmap_chain(kvm, rev, rmap, index, 0);
}
---------------------------------------------> if we try_to_unmap on
pfn at here, then @r contains a invalid pfn
hptep[1] = r;
eieio();
hptep[0] = hpte[0];
asm volatile("ptesync" : : : "memory");
Thx.
Fan
On Mon, Jul 28, 2014 at 2:42 PM, Benjamin Herrenschmidt
<[email protected]> wrote:
> 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 <[email protected]>
>> ---
>> 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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