var swiper = new Swiper('.swiper-container', {
    direction: 'vertical',
});
var startScroll, touchStart, touchCurrent;
swiper.slides.on('touchstart', function (e) {
    startScroll = this.scrollTop;
    touchStart = e.targetTouches[0].pageY;
}, true);
swiper.slides.on('touchmove', function (e) {
    touchCurrent = e.targetTouches[0].pageY;
    var touchesDiff = touchCurrent - touchStart;
    var slide = this;
    var onlyScrolling =
            ( slide.scrollHeight > slide.offsetHeight ) && //allow only when slide is scrollable
            (
                ( touchesDiff < 0 && startScroll === 0 ) || //start from top edge to scroll bottom
                ( touchesDiff > 0 && startScroll === ( slide.scrollHeight - slide.offsetHeight ) ) || //start from bottom edge to scroll top
                ( startScroll > 0 && startScroll < ( slide.scrollHeight - slide.offsetHeight ) ) //start from the middle
            );
    if (onlyScrolling) {
        e.stopPropagation();
    }
}, true);

<style>
.swiper-slide {
  overflow-y: auto;
}
</style>