2022-12-13 00:23:39

by Sean Christopherson

Subject: [PATCH 03/14] KVM: selftests: Fix divide-by-zero bug in memslot_perf_test

Check that the number of pages per slot is non-zero in get_max_slots()
prior to computing the remaining number of pages. clang generates code
that uses an actual DIV for calculating the remaining, which causes a #DE
if the total number of pages is less than the number of slots.

traps: memslot_perf_te[97611] trap divide error ip:4030c4 sp:7ffd18ae58f0
error:0 in memslot_perf_test[401000+cb000]

Fixes: a69170c65acd ("KVM: selftests: memslot_perf_test: Report optimal memory slots")
Signed-off-by: Sean Christopherson <[email protected]>
---
tools/testing/selftests/kvm/memslot_perf_test.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c
index e698306bf49d..e6587e193490 100644
--- a/tools/testing/selftests/kvm/memslot_perf_test.c
+++ b/tools/testing/selftests/kvm/memslot_perf_test.c
@@ -265,6 +265,9 @@ static uint64_t get_max_slots(struct vm_data *data, uint32_t host_page_size)
slots = data->nslots;
while (--slots > 1) {
pages_per_slot = mempages / slots;
+ if (!pages_per_slot)
+ continue;
+
rempages = mempages % pages_per_slot;
if (check_slot_pages(host_page_size, guest_page_size,
pages_per_slot, rempages))
--
2.39.0.rc1.256.g54fd8350bd-goog

2022-12-13 10:20:02

by Philippe Mathieu-Daudé

Subject: Re: [PATCH 03/14] KVM: selftests: Fix divide-by-zero bug in memslot_perf_test

On 13/12/22 01:16, Sean Christopherson wrote:
> Check that the number of pages per slot is non-zero in get_max_slots()
> prior to computing the remaining number of pages. clang generates code
> that uses an actual DIV for calculating the remaining, which causes a #DE
> if the total number of pages is less than the number of slots.
>
> traps: memslot_perf_te[97611] trap divide error ip:4030c4 sp:7ffd18ae58f0
> error:0 in memslot_perf_test[401000+cb000]
>
> Fixes: a69170c65acd ("KVM: selftests: memslot_perf_test: Report optimal memory slots")
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> tools/testing/selftests/kvm/memslot_perf_test.c | 3 +++
> 1 file changed, 3 insertions(+)

Reviewed-by: Philippe Mathieu-Daudé <[email protected]>