This is more of a theological question since the text itself doesn't really make this explicit. The English translation you've given is a good rendering of this passage into English. The text is clear that "you have [already] been saved," as it is perfect (completed action), but whether faith was a one-time event or ongoing necessity is not immediately clear from this verse. However, it doesn't seem to be our concern based on the remainder of this passage:
And this is not your own doing; it is the gift of God, not a result
of works, so that no one may boast.
In other words, whether this is based on past faith or a continuation of it, it seems to be a gift from God that is not a result of our own effort.
In the Greek, "faith" is essentially just the noun form of the verb translated into English as "to believe." Thus it is not as abstract as we sometimes make it. The verb could also be translated to illustrate this as "faithing," but this is invalid English. The other issue is that Greek authors frequently consider "belief" to be synonymous with "obedience," which are concepts we tend to separate in our minds. However, at least from my study of Greek, I don't believe the aspect (aktionsart) of the verb πιστεύω is consistently telic or atelic throughout scripture, but I believe focusing on who performs/accomplishes/possesses soteriological faith can shed the most light on this, in addition to looking at aspect (keeping in mind that we must study both the verb and the noun forms within their respective contexts).
Soteriological faith is not solely an issue of aspect, but also whose faith it is
If you were interested in this, you would need to look at how the word πίστις (faith) is used elsewhere in scripture and to whom soteriological faith is ascribed. There is a contemporary scholarly controversy about this very question known as the πίστις Χρίστου (pistis Christou) debate. To briefly summarize the debate, there is conflict over how the phrase πίστις Χρίστου should be translated in scripture, specifically whether Χρίστου is objective or subjective genitive. Consider Galatians 2:16; in the objective genitive it reads (ESV):
...we know that a person is not justified by works of the law but
through faith in Jesus Christ....
But in the subjective genitive this same passage reads (NET):
...we know that no one is justified by the works of the law but by the
faithfulness of Jesus Christ....
The NET translators explain this in their notes on the verse:
A decision is difficult here. Though traditionally translated “faith
in Jesus Christ,” an increasing number of NT scholars are arguing that
πίστις Χριστοῦ (pisti" Cristou) and similar phrases in Paul (here and
in v. 20; Rom 3:22, 26; Gal 3:22; Eph 3:12; Phil 3:9) involve a
subjective genitive and mean “Christ’s faith” or “Christ’s
faithfulness” (cf., e.g., G. Howard, “The ‘Faith of Christ’,” ExpTim
85 : 212-15; R. B. Hays, The Faith of Jesus Christ [SBLDS];
Morna D. Hooker, “Πίστις Χριστοῦ,” NTS 35 : 321-42). Noteworthy
among the arguments for the subjective genitive view is that when
πίστις takes a personal genitive it is almost never an objective
genitive (cf. Matt 9:2, 22, 29; Mark 2:5; 5:34; 10:52; Luke 5:20;
7:50; 8:25, 48; 17:19; 18:42; 22:32; Rom 1:8; 12; 3:3; 4:5, 12, 16; 1
Cor 2:5; 15:14, 17; 2 Cor 10:15; Phil 2:17; Col 1:4; 2:5; 1 Thess 1:8;
3:2, 5, 10; 2 Thess 1:3; Titus 1:1; Phlm 6; 1 Pet 1:9, 21; 2 Pet 1:5).
On the other hand, the objective genitive view has its adherents: A.
Hultgren, “The Pistis Christou Formulations in Paul,” NovT 22 (1980):
248-63; J. D. G. Dunn, “Once More, ΠΙΣΤΙΣ ΧΡΙΣΤΟΥ,” SBL Seminar
Papers, 1991, 730-44. Most commentaries on Romans and Galatians
usually side with the objective view.
This is a big difference: is Christ the object or subject of faith, and what does this mean for our understanding of salvation (soteriology)? I recommend this book or any of the myriad of academic papers written on the topic for a more in depth understanding. This along with a thorough study of the aspect of the verb πιστεύω in its various contexts would help you answer this question. Unfortunately, this is more the topic of academic papers and published books than Stack Exchange answers, as to do this justice would require exhaustive study - and no doubt good books and papers are being written on both sides of the fence. I know this doesn't answer the question, per se, but I hope I have given you a sufficient introduction to the depth of the problem and where you can find resources to learn more.