git: 7a8440bf0894 - main - amd64: make LA57 mode for a process opt-in by default

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=7a8440bf0894f910f871e91a660a9f66dbb23f0b

commit 7a8440bf0894f910f871e91a660a9f66dbb23f0b
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2025-04-19 10:55:18 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2025-04-27 22:31:59 +0000

    amd64: make LA57 mode for a process opt-in by default
    
    The vm.pmap.prefer_la48 manages the mode.
    
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D49913
---
 sys/amd64/amd64/elf_machdep.c | 4 +++-
 sys/amd64/amd64/pmap.c        | 9 +++++++++
 sys/amd64/include/md_var.h    | 1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
index 0e6c8d310dfd..6cc2d58bbbcc 100644
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -170,11 +170,13 @@ freebsd_brand_info_la57_img_compat(const struct image_params *imgp,
 {
 	if ((imgp->proc->p_md.md_flags & P_MD_LA57) != 0)
 		return (true);
+	if (fctl0 != NULL && (*fctl0 & NT_FREEBSD_FCTL_LA57) != 0)
+		return (true);
 	if (fctl0 == NULL || (*fctl0 & NT_FREEBSD_FCTL_LA48) != 0)
 		return (false);
 	if ((imgp->proc->p_md.md_flags & P_MD_LA48) != 0)
 		return (false);
-	return (true);
+	return (!prefer_uva_la48);
 }
 
 static Elf64_Brandinfo freebsd_brand_info_la48 = {
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 9ff630de5b6e..4ad1335329da 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -431,6 +431,15 @@ SYSCTL_INT(_vm_pmap, OID_AUTO, la57, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
     &la57, 0,
     "5-level paging for host is enabled");
 
+/*
+ * The default value is needed in order to preserve compatibility with
+ * some userspace programs that put tags into sign-extended bits.
+ */
+int prefer_uva_la48 = 1;
+SYSCTL_INT(_vm_pmap, OID_AUTO, prefer_uva_la48, CTLFLAG_RDTUN,
+    &prefer_uva_la48, 0,
+    "Userspace maps are limited to LA48 unless otherwise configured");
+
 static bool
 pmap_is_la57(pmap_t pmap)
 {
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
index ce6f05fa1739..b6ddc6eaaebe 100644
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -50,6 +50,7 @@ extern vm_paddr_t intel_graphics_stolen_base;
 extern vm_paddr_t intel_graphics_stolen_size;
 
 extern int la57;
+extern int prefer_uva_la48;
 
 extern vm_paddr_t kernphys;
 extern vm_paddr_t KERNend;