Re: [PATCH] accel/kvm/kvm-all: Fix wrong return code handling in dirty log code

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/01/21 09:43, Thomas Huth wrote:
> The kvm_vm_ioctl() wrapper already returns -errno if the ioctl itself
> returned -1, so the callers of kvm_vm_ioctl() should not check for -1
> but for a value < 0 instead.
> 
> This problem has been fixed once already in commit b533f658a98325d0e4
> but that commit missed that the ENOENT error code is not fatal for
> this ioctl, so the commit has been reverted in commit 50212d6346f33d6e
> since the problem occurred close to a pending release at that point
> in time. The plan was to fix it properly after the release, but it
> seems like this has been forgotten. So let's do it now finally instead.
> 
> Resolves: https://bugs.launchpad.net/qemu/+bug/1294227
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   accel/kvm/kvm-all.c | 21 ++++++++++++---------
>   1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 3feb17d965..7224596932 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -668,16 +668,19 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
>   
>           d.dirty_bitmap = mem->dirty_bmap;
>           d.slot = mem->slot | (kml->as_id << 16);
> -        if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
> -            DPRINTF("ioctl failed %d\n", errno);
> -            ret = -1;
> +        ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
> +        if (ret == -ENOENT) {
> +            /* kernel does not have dirty bitmap in this slot */
> +            ret = 0;
> +        } else if (ret < 0) {
> +            error_report("ioctl KVM_GET_DIRTY_LOG failed: %d", errno);
>               goto out;
> +        } else {
> +            subsection.offset_within_region += slot_offset;
> +            subsection.size = int128_make64(slot_size);
> +            kvm_get_dirty_pages_log_range(&subsection, d.dirty_bitmap);
>           }
>   
> -        subsection.offset_within_region += slot_offset;
> -        subsection.size = int128_make64(slot_size);
> -        kvm_get_dirty_pages_log_range(&subsection, d.dirty_bitmap);
> -
>           slot_offset += slot_size;
>           start_addr += slot_size;
>           size -= slot_size;
> @@ -774,8 +777,8 @@ static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start,
>       d.num_pages = bmap_npages;
>       d.slot = mem->slot | (as_id << 16);
>   
> -    if (kvm_vm_ioctl(s, KVM_CLEAR_DIRTY_LOG, &d) == -1) {
> -        ret = -errno;
> +    ret = kvm_vm_ioctl(s, KVM_CLEAR_DIRTY_LOG, &d);
> +    if (ret < 0 && ret != -ENOENT) {
>           error_report("%s: KVM_CLEAR_DIRTY_LOG failed, slot=%d, "
>                        "start=0x%"PRIx64", size=0x%"PRIx32", errno=%d",
>                        __func__, d.slot, (uint64_t)d.first_page,
> 

Queued, thanks.

Paolo