* [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT
@ 2014-07-28 6:09 Liu Ping Fan
2014-07-28 6:42 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 5+ messages in thread
From: Liu Ping Fan @ 2014-07-28 6:09 UTC (permalink / raw)
To: linuxppc-dev, kvm-ppc; +Cc: Paul Mackerras, Alexander Graf
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.
Signed-off-by: Liu Ping Fan <pingfank@linux•vnet.ibm.com>
---
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);
--
1.8.1.4
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT
2014-07-28 6:09 [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT Liu Ping Fan
@ 2014-07-28 6:42 ` Benjamin Herrenschmidt
2014-07-28 7:58 ` Liu ping fan
0 siblings, 1 reply; 5+ messages in thread
From: Benjamin Herrenschmidt @ 2014-07-28 6:42 UTC (permalink / raw)
To: Liu Ping Fan; +Cc: Paul Mackerras, linuxppc-dev, Alexander Graf, kvm-ppc
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@linux•vnet.ibm.com>
> ---
> 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);
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT
2014-07-28 6:42 ` Benjamin Herrenschmidt
@ 2014-07-28 7:58 ` Liu ping fan
2014-07-29 6:57 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 5+ messages in thread
From: Liu ping fan @ 2014-07-28 7:58 UTC (permalink / raw)
To: Benjamin Herrenschmidt
Cc: Paul Mackerras, linuxppc-dev, Alexander Graf, kvm-ppc
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
<benh@kernel•crashing.org> 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 <pingfank@linux•vnet.ibm.com>
>> ---
>> 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);
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT
2014-07-28 7:58 ` Liu ping fan
@ 2014-07-29 6:57 ` Benjamin Herrenschmidt
2014-07-29 8:07 ` Liu ping fan
0 siblings, 1 reply; 5+ messages in thread
From: Benjamin Herrenschmidt @ 2014-07-29 6:57 UTC (permalink / raw)
To: Liu ping fan; +Cc: Paul Mackerras, linuxppc-dev, Alexander Graf, kvm-ppc
On Mon, 2014-07-28 at 15:58 +0800, Liu ping fan wrote:
> 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");
If that was the case we would have the same race in kvmppc_do_h_enter().
I think the fact that the HPTE is locked will prevent the race, ie,
HPTE_V_HVLOCK is set until hptep[0] is written to.
If I look at at the unmap case, my understanding is that it uses
kvm_unmap_rmapp() which will also lock the HPTE (try_lock_hpte)
and so shouldn't have a race vs the above code.
Or do you see a race I don't ?
Cheers,
Ben.
> Thx.
> Fan
>
> On Mon, Jul 28, 2014 at 2:42 PM, Benjamin Herrenschmidt
> <benh@kernel•crashing.org> 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 <pingfank@linux•vnet.ibm.com>
> >> ---
> >> 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);
> >
> >
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT
2014-07-29 6:57 ` Benjamin Herrenschmidt
@ 2014-07-29 8:07 ` Liu ping fan
0 siblings, 0 replies; 5+ messages in thread
From: Liu ping fan @ 2014-07-29 8:07 UTC (permalink / raw)
To: Benjamin Herrenschmidt
Cc: Paul Mackerras, linuxppc-dev, Alexander Graf, kvm-ppc
On Tue, Jul 29, 2014 at 2:57 PM, Benjamin Herrenschmidt
<benh@kernel•crashing.org> wrote:
> On Mon, 2014-07-28 at 15:58 +0800, Liu ping fan wrote:
>> 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");
>
> If that was the case we would have the same race in kvmppc_do_h_enter().
>
> I think the fact that the HPTE is locked will prevent the race, ie,
> HPTE_V_HVLOCK is set until hptep[0] is written to.
>
> If I look at at the unmap case, my understanding is that it uses
> kvm_unmap_rmapp() which will also lock the HPTE (try_lock_hpte)
> and so shouldn't have a race vs the above code.
>
Yes, you are right :)
Thx,
Fan
> Or do you see a race I don't ?
>
> Cheers,
> Ben.
>
>> Thx.
>> Fan
>>
>> On Mon, Jul 28, 2014 at 2:42 PM, Benjamin Herrenschmidt
>> <benh@kernel•crashing.org> 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 <pingfank@linux•vnet.ibm.com>
>> >> ---
>> >> 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);
>> >
>> >
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2014-07-29 8:07 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2014-07-28 6:09 [PATCH] powerpc: kvm: make the setup of hpte under the protection of KVMPPC_RMAP_LOCK_BIT Liu Ping Fan
2014-07-28 6:42 ` Benjamin Herrenschmidt
2014-07-28 7:58 ` Liu ping fan
2014-07-29 6:57 ` Benjamin Herrenschmidt
2014-07-29 8:07 ` Liu ping fan
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