Re: [PATCH v13 4/6] KVM: s390: pv: avoid export before import if possible

[Janosch Frank]

On 8/10/22 14:56, Claudio Imbrenda wrote:
> If the appropriate UV feature bit is set, there is no need to perform
> an export before import.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Reviewed-by: Nico Boehr <nrb@xxxxxxxxxxxxx>
> ---
>   arch/s390/kernel/uv.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index f9810d2a267c..b455646c8d74 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -255,6 +255,8 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
>    */
>   static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_struct *mm)
>   {
The misc feature indicates that the UV will automatically transfer 
ownership from one protected VM to another when importing a shared page.


Other than that:
Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>


> +	if (test_bit_inv(BIT_UV_FEAT_MISC, &uv_info.uv_feature_indications))
> +		return false;
>   	if (uvcb->cmd == UVC_CMD_UNPIN_PAGE_SHARED)
>   		return false;
>   	return atomic_read(&mm->context.protected_count) > 1;