314131 2026-05-05 15:34:39 -0700 [Site Isolation] Only reuse target back/forward item's process when navigating the main frame 2026-05-06 14:17:27 -0700 1 1 1 Unclassified WebKit New Bugs WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 basuke basuke webkit-bug-importer oldest_to_newest 2207820 0 basuke 2026-05-05 15:34:39 -0700 In WebProcessPool::processForNavigationInternal, when handling a back/forward navigation, the code looks up targetItem->lastProcessIdentifier() and reuses that process for any frame — including subframes. Under Site Isolation with multi-process BFCache enabled, subframe back/forward navigations can reach this code path. The target back/forward item's lastProcessIdentifier is always the main frame's process, so using it for a subframe navigation picks the wrong process. Guard the lastProcessIdentifier lookup with frame.isMainFrame() so only main-frame navigations take this path. Subframe back/forward navigations fall through to the normal process-selection logic, which selects the appropriate site-matched process for the subframe. Prep patch for rdar://173743733 (multi-process BFCache restoration under Site Isolation). 2207866 1 basuke 2026-05-05 16:45:54 -0700 <rdar://problem/176305015> 2207867 2 basuke 2026-05-05 16:46:10 -0700 Pull request: https://github.com/WebKit/WebKit/pull/64311 2208280 3 ews-feeder 2026-05-06 14:17:25 -0700 Committed 312735@main (4fd10b14732e): <https://commits.webkit.org/312735@main> Reviewed commits have been landed. Closing PR #64311 and removing active labels.