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@xxxxxxxxxxxxxxx # v4.1+
Fixes: 35307b9a5f7e ("arm/arm64: KVM: Implement Stage-2 page aging")
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
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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