I have tried with the code you provided , but ALL option isn't working , below is my sample xml for my entire dashboard . let me know if I am missing anything here .
<form>
<label>My test dropdown</label>
<search id="baseSearchHostFilter">
<query>| tstats count where index="abc" AND host=*$service$* AND host=*$env$* by host
| stats values(host) as host
| nomv host
| eval host=replace(host," ",",")
| table host
<earliest>-7d@h</earliest>
<latest>now</latest>
<done>
<set token="tokAllFilteredHosts">$result.host$</set>
</done>
<input type="dropdown" token="service" searchWhenChanged="true">
<label>Select service</label>
<choice value="service1">service1</choice>
<choice value="service2">service2</choice>
<fieldForLabel>service</fieldForLabel>
<fieldForValue>service</fieldForValue>
</input>
<input type="dropdown" token="env" searchWhenChanged="true">
<label>Select Environment</label>
<choice value="DEV">DEV</choice>
<choice value="QA">QA</choice>
<choice value="PROD">PROD</choice>
<fieldForLabel>env</fieldForLabel>
<fieldForValue>env</fieldForValue>
</input>
<input type="dropdown" token="tokHostDropDown" searchWhenChanged="true">
<label>Select Host</label>
<fieldForLabel>host</fieldForLabel>
<fieldForValue>host</fieldForValue>
<search base="baseSearchHostFilter">
<query>| makemv host delim=","
| mvexpand host
</query>
</search>
<change>
<condition label="All">
<set token="tokHost">$tokAllFilteredHosts$</set>
</condition>
<condition>
<set token="tokHost">$value$</set>
</condition>
</change>
<choice value="*">All</choice>
</input>
<panel>
<event>
<search>
<query>index="abc" host=$tokHostDropDown$</query>
<earliest>$time_range.earliest$</earliest>
<latest>$time_range.latest$</latest>
</search>
<option name="list.drilldown">full</option>
<option name="refresh.display">progressbar</option>
</event>
</panel>
... View more