The Crisis on Infinite Earths crossover event is changing one aspect of Smallville's canon but leaving everything else the way it was. The upcoming crossover will give the Kent Farm back to Clark Kent (Tom Welling), who sold it in season 10. The Kent Farm was Clark's home for most of the series. It was even used as the home of the Earth-38 Superman (Tyler Hoechlin) in last year's Elseworlds crossover.
The farm has been in the Kent family for four generations, including Clark. For years, it was run by his father, Jonathan (John Schneider), who often struggled with financial problems and keeping the farm afloat. The farm went to Martha (Annette O'Toole) after Jonathan's tragic death in season 5. In Smallville's tenth and final season, Martha gave Clark the deed to the Kent Farm as a wedding present. Clark pondered over what to do about the farm, and eventually decided to sell it. Clark and Lois (Erica Durance) then moved into a Metropolis apartment. In the two-part series finale, Clark claimed that he found a buyer for the farm. But in the comic book continuation, Smallville Season 11, Clark gets the farm back.
Arrowverse producer Marc Guggenheim said in a tweet that Smallville Season 11 will be treated as canon but not directly referenced, with the exception of the Kent Farm. As Guggenheim notes, the Kent Farm was bought back "off-camera." It was already suspected that the Kent Farm would appear in the crossover, since it's been seen in set photos with Tom Welling, Elizabeth Tulloch, Erica Durance, and Tyler Hoechlin. Bringing Welling back as Clark Kent is huge, but it means so much more to Smallville fans that the Kent Farm returns as well. It was the landmark location of the entire series and the one that viewers most identify with Smallville. So it's only natural that it returns in the Arrowverse crossover. After all, the Elseworlds crossover specifically chose to play the Smallville theme song when showing the Kent Farm.
Through the show's ten-season run there have been multiple recurring locations, such as Lex's mansion, The Talon, Watchtower, the Daily Planet, LutherCorp, and the Kawatche Caves, but none are more iconic to Smallville than the Kent Farm, the place where Clark first began his journey in the pilot episode. It was at the Kent Farm where fans would see Jonathan give Clark fatherly advice, Lana (Kristin Kreuk) visit Clark in his loft, and more. Clark lived there for almost the entirety of the series, and it was also the temporary home of Lois, Kara (Laura Vandervoort), and Lana. The Kent Farm is one location that remained a key part of the show throughout its entire run.
This could be why Crisis on Infinite Earths is keeping the Kent Farm. For the Arrowverse to incorporate the show into its the crossover, it may have felt necessary for Crisis on Infinite Earths to make use of Smallville's most important set piece.