Re: [PATCH v2 1/1] migration/dirtyrate: Fix segmentation fault

[mii]

On 2024/04/24 10:28, Yong Huang wrote:

On Tue, Apr 23, 2024 at 9:35 PM Peter Xu <peterx@redhat.com> wrote:

On Tue, Apr 23, 2024 at 09:13:08AM +0000, Masato Imai wrote:
> When the KVM acceleration parameter is not set, executing calc_dirty_rate
> with the -r or -b option results in a segmentation fault due to accessing
> a null kvm_state pointer in the kvm_dirty_ring_enabled function.
> This commit adds a check for kvm_enabled to prevent segmentation faults.
>
> Signed-off-by: Masato Imai <mii@sfc.wide.ad.jp>
> ---
>  migration/dirtyrate.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
> index 1d2e85746f..2a7df52519 100644
> --- a/migration/dirtyrate.c
> +++ b/migration/dirtyrate.c
> @@ -799,6 +799,13 @@ void qmp_calc_dirty_rate(int64_t calc_time,
>       * dirty ring mode only works when kvm dirty ring is enabled.
>       * on the contrary, dirty bitmap mode is not.
>       */
> +    if (!kvm_enabled() &&
> +        (mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING ||
> +         mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP)) {
> +        error_setg(errp, "mode %s requires kvm to be enabled.",
> +                         DirtyRateMeasureMode_str(mode));
> +        return;
> +    }

Logically dirty bitmap should work with tcg.  So the other option is to let
kvm_dirty_ring_enabled() check kvm_state too and return false if
kvm_state==NULL?

Agree, better solution

>      if (((mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) &&
>          !kvm_dirty_ring_enabled()) ||
>          ((mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP) &&
> --
> 2.34.1
>

--
Peter Xu

Thanks,

Yong

--

Best regards

Thank you for the review. I agree with that solution.

Update will be like:

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 931f74256e..0f8499365d 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2312,6 +2312,9 @@ bool kvm_vcpu_id_is_valid(int vcpu_id)

 bool kvm_dirty_ring_enabled(void)
 {
+    if (kvm_state == NULL) {
+        return false;
+    }
     return kvm_state->kvm_dirty_ring_size ? true : false;
 }