commit d75cb9a50c104ad2d50ecd456657ef1cf002810b
Author: Mark Johnston <markjdb@gmail.com>
Date:   Tue Nov 10 21:03:45 2020 -0500

    kstack: Hide the guard page from UMA
    
    Otherwise we can't determine domain affinity properly.

diff --git a/sys/vm/vm_glue.c b/sys/vm/vm_glue.c
index a2500828eae4..c927ede3b45f 100644
--- a/sys/vm/vm_glue.c
+++ b/sys/vm/vm_glue.c
@@ -370,8 +370,10 @@ vm_thread_new(struct thread *td, int pages)
 		pages = KSTACK_MAX_PAGES;
 
 	ks = 0;
-	if (pages == kstack_pages && kstack_cache != NULL)
+	if (pages == kstack_pages && kstack_cache != NULL) {
 		ks = (vm_offset_t)uma_zalloc(kstack_cache, M_NOWAIT);
+		ks -= KSTACK_GUARD_PAGES * PAGE_SIZE;
+	}
 
 	/*
 	 * Ensure that kstack objects can draw pages from any memory
@@ -401,10 +403,12 @@ vm_thread_dispose(struct thread *td)
 	ks = td->td_kstack;
 	td->td_kstack = 0;
 	td->td_kstack_pages = 0;
-	if (pages == kstack_pages)
+	if (pages == kstack_pages) {
+		ks += KSTACK_GUARD_PAGES * PAGE_SIZE;
 		uma_zfree(kstack_cache, (void *)ks);
-	else
+	} else {
 		vm_thread_stack_dispose(ks, pages);
+	}
 }
 
 /*
@@ -440,6 +444,7 @@ static int
 kstack_import(void *arg, void **store, int cnt, int domain, int flags)
 {
 	struct domainset *ds;
+	vm_offset_t ks;
 	int i;
 
 	if (domain == UMA_ANYDOMAIN)
@@ -448,7 +453,8 @@ kstack_import(void *arg, void **store, int cnt, int domain, int flags)
 		ds = DOMAINSET_PREF(domain);
 
 	for (i = 0; i < cnt; i++) {
-		store[i] = (void *)vm_thread_stack_create(ds, kstack_pages);
+		ks = vm_thread_stack_create(ds, kstack_pages);
+		store[i] = (void *)(ks + KSTACK_GUARD_PAGES * PAGE_SIZE);
 		if (store[i] == NULL)
 			break;
 	}
@@ -463,6 +469,7 @@ kstack_release(void *arg, void **store, int cnt)
 
 	for (i = 0; i < cnt; i++) {
 		ks = (vm_offset_t)store[i];
+		ks -= KSTACK_GUARD_PAGES * PAGE_SIZE;
 		vm_thread_stack_dispose(ks, kstack_pages);
 	}
 }