* [PATCH] KVM: arm/arm64: Fix young bit from mmu notifier
@ 2020-01-21 5:56 Gavin Shan
2020-01-21 13:28 ` Marc Zyngier
0 siblings, 1 reply; 3+ messages in thread
From: Gavin Shan @ 2020-01-21 5:56 UTC (permalink / raw)
To: kvmarm, linux-arm-kernel; +Cc: maz
kvm_test_age_hva() is called upon mmu_notifier_test_young(), but wrong
address range has been passed to handle_hva_to_gpa(). With the wrong
address range, no young bits will be checked in handle_hva_to_gpa().
It means zero is always returned from mmu_notifier_test_young().
This fixes the issue by passing correct address range to the underly
function handle_hva_to_gpa(), so that the hardware young (access) bit
will be visited.
Cc: stable@vger.kernel.org # v4.1+
Fixes: 35307b9a5f7e ("arm/arm64: KVM: Implement Stage-2 page aging")
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
virt/kvm/arm/mmu.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 0b32a904a1bb..a2777efb558e 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -2147,7 +2147,8 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
if (!kvm->arch.pgd)
return 0;
trace_kvm_test_age_hva(hva);
- return handle_hva_to_gpa(kvm, hva, hva, kvm_test_age_hva_handler, NULL);
+ return handle_hva_to_gpa(kvm, hva, hva + PAGE_SIZE,
+ kvm_test_age_hva_handler, NULL);
}
void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu)
--
2.23.0
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: arm/arm64: Fix young bit from mmu notifier
2020-01-21 5:56 [PATCH] KVM: arm/arm64: Fix young bit from mmu notifier Gavin Shan
@ 2020-01-21 13:28 ` Marc Zyngier
2020-01-21 23:07 ` Gavin Shan
0 siblings, 1 reply; 3+ messages in thread
From: Marc Zyngier @ 2020-01-21 13:28 UTC (permalink / raw)
To: Gavin Shan; +Cc: kvmarm, linux-arm-kernel
On 2020-01-21 05:56, Gavin Shan wrote:
> kvm_test_age_hva() is called upon mmu_notifier_test_young(), but wrong
> address range has been passed to handle_hva_to_gpa(). With the wrong
> address range, no young bits will be checked in handle_hva_to_gpa().
> It means zero is always returned from mmu_notifier_test_young().
>
> This fixes the issue by passing correct address range to the underly
> function handle_hva_to_gpa(), so that the hardware young (access) bit
> will be visited.
>
> Cc: stable@vger.kernel.org # v4.1+
> Fixes: 35307b9a5f7e ("arm/arm64: KVM: Implement Stage-2 page aging")
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> virt/kvm/arm/mmu.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 0b32a904a1bb..a2777efb558e 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -2147,7 +2147,8 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned
> long hva)
> if (!kvm->arch.pgd)
> return 0;
> trace_kvm_test_age_hva(hva);
> - return handle_hva_to_gpa(kvm, hva, hva, kvm_test_age_hva_handler,
> NULL);
> + return handle_hva_to_gpa(kvm, hva, hva + PAGE_SIZE,
> + kvm_test_age_hva_handler, NULL);
> }
>
> void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu)
I knew this start/end thing (instead of start/size) would bite us
one of these days. Terribly embarrassing. On the other hand, who
really wants to swap things out? ;-)
Out of curiosity, how did you find this one?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: arm/arm64: Fix young bit from mmu notifier
2020-01-21 13:28 ` Marc Zyngier
@ 2020-01-21 23:07 ` Gavin Shan
0 siblings, 0 replies; 3+ messages in thread
From: Gavin Shan @ 2020-01-21 23:07 UTC (permalink / raw)
To: Marc Zyngier; +Cc: kvmarm, linux-arm-kernel
On 1/22/20 12:28 AM, Marc Zyngier wrote:
> On 2020-01-21 05:56, Gavin Shan wrote:
>> kvm_test_age_hva() is called upon mmu_notifier_test_young(), but wrong
>> address range has been passed to handle_hva_to_gpa(). With the wrong
>> address range, no young bits will be checked in handle_hva_to_gpa().
>> It means zero is always returned from mmu_notifier_test_young().
>>
>> This fixes the issue by passing correct address range to the underly
>> function handle_hva_to_gpa(), so that the hardware young (access) bit
>> will be visited.
>>
>> Cc: stable@vger.kernel.org # v4.1+
>> Fixes: 35307b9a5f7e ("arm/arm64: KVM: Implement Stage-2 page aging")
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>> virt/kvm/arm/mmu.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index 0b32a904a1bb..a2777efb558e 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -2147,7 +2147,8 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
>> if (!kvm->arch.pgd)
>> return 0;
>> trace_kvm_test_age_hva(hva);
>> - return handle_hva_to_gpa(kvm, hva, hva, kvm_test_age_hva_handler, NULL);
>> + return handle_hva_to_gpa(kvm, hva, hva + PAGE_SIZE,
>> + kvm_test_age_hva_handler, NULL);
>> }
>>
>> void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu)
>
> I knew this start/end thing (instead of start/size) would bite us
> one of these days. Terribly embarrassing. On the other hand, who
> really wants to swap things out? ;-)
>
> Out of curiosity, how did you find this one?
>
Well, it's hard to tell who really wants to swap things out. Something I
was involved previously: user daemon is started to scan the accessed pages
periodically, in order to determine the least accessed pages. These least
access anonymous pages are migrated to low-cost storage (e.g. NVDIMM). This
helps on balance of performance and cost.
It's found when reading code. After that, I wrote some code (as below) to
double confirm:
(1) locate qemu process and the corresponding vma because the VM is started
with "mem-path=/tmp/virtiofs/backup-file". "backup-file" is the key in
the location.
(2) iterate the virtual space of the vma by mmu_notifier_test_young(), none
of return values is 1 (accessed). It seems it's not correct.
With the patch applied and rerun above code, mmu_notifier_test_young() returns
1 (accessed) on some pages.
Thanks,
Gavin
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2020-01-21 13:28 ` Marc Zyngier
2020-01-21 23:07 ` Gavin Shan
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