git: 532c8d3f90b9 - stable/15 - amd64: add LASS support

The branch stable/15 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=532c8d3f90b95fb13b320cdfdc89e3d7d08875db

commit 532c8d3f90b95fb13b320cdfdc89e3d7d08875db
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2024-10-24 02:12:25 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2026-02-18 08:00:04 +0000

    amd64: add LASS support
    
    (cherry picked from commit 89589b6d3fbac43eb7c6b3cdbdd6f077888b2142)
---
 sys/amd64/amd64/efirt_machdep.c |  4 ++++
 sys/amd64/amd64/initcpu.c       | 13 +++++++++++++
 sys/amd64/amd64/machdep.c       |  1 +
 sys/amd64/amd64/pmap.c          |  9 +++++++++
 sys/amd64/include/md_var.h      |  1 +
 5 files changed, 28 insertions(+)

diff --git a/sys/amd64/amd64/efirt_machdep.c b/sys/amd64/amd64/efirt_machdep.c
index fe5d60c978dd..203b2b264587 100644
--- a/sys/amd64/amd64/efirt_machdep.c
+++ b/sys/amd64/amd64/efirt_machdep.c
@@ -348,6 +348,8 @@ efi_arch_enter(void)
 	 */
 	if (!pmap_pcid_enabled)
 		invltlb();
+	if (lass_enabled)
+		load_cr4(rcr4() & ~CR4_LASS);
 	return (0);
 }
 
@@ -357,6 +359,8 @@ efi_arch_leave(void)
 	pmap_t curpmap;
 	uint64_t cr3;
 
+	if (lass_enabled)
+		load_cr4(rcr4() | CR4_LASS);
 	curpmap = &curproc->p_vmspace->vm_pmap;
 	cr3 = curpmap->pm_cr3;
 	if (pmap_pcid_enabled) {
diff --git a/sys/amd64/amd64/initcpu.c b/sys/amd64/amd64/initcpu.c
index 7f317674907e..4c57c27596ad 100644
--- a/sys/amd64/amd64/initcpu.c
+++ b/sys/amd64/amd64/initcpu.c
@@ -290,6 +290,19 @@ initializecpu(void)
 	if (cpu_stdext_feature2 & CPUID_STDEXT2_PKU)
 		cr4 |= CR4_PKE;
 
+	/*
+	 * Any CPU having Linear Address Space Separation (LASS)
+	 * should have SMAP, but check it to be sure.  Otherwise
+	 * userspace accesses from kernel cannot work.
+	 */
+	if (IS_BSP() && (cpu_stdext_feature4 & CPUID_STDEXT4_LASS) != 0 &&
+	    (cpu_stdext_feature & CPUID_STDEXT_SMAP) != 0) {
+		lass_enabled = 1;
+		TUNABLE_INT_FETCH("hw.lass", &lass_enabled);
+	}
+	if (lass_enabled)
+		cr4 |= CR4_LASS;
+
 	/*
 	 * If SMEP is present, we only need to flush RSB (by default)
 	 * on context switches, to prevent cross-process ret2spec
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index e56de986ccba..20d221279bd3 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -204,6 +204,7 @@ int cold = 1;
 long Maxmem = 0;
 long realmem = 0;
 int late_console = 1;
+int lass_enabled = 0;
 
 struct kva_md_info kmi;
 
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 243a6625bece..8695dd61316e 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -1737,6 +1737,7 @@ pmap_bootstrap_la57(vm_paddr_t *firstaddr)
 {
 	void (*la57_tramp)(uint64_t pml5);
 	pml5_entry_t *pt;
+	uint64_t cr4;
 
 	if ((cpu_stdext_feature2 & CPUID_STDEXT2_LA57) == 0)
 		return;
@@ -1757,8 +1758,16 @@ pmap_bootstrap_la57(vm_paddr_t *firstaddr)
 	    KERNSTART + amd64_loadaddr());
 	printf("Calling la57 trampoline at %p, KPML5phys %#lx ...",
 	    la57_tramp, KPML5phys);
+	if (lass_enabled) {
+		cr4 = rcr4();
+		load_cr4(cr4 & ~CR4_LASS);
+	}
 	la57_tramp(KPML5phys);
 	printf(" alive in la57 mode\n");
+	if (lass_enabled) {
+		cr4 = rcr4();
+		load_cr4(cr4 | CR4_LASS);
+	}
 }
 
 static void
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
index 19eab48168f7..7bb8ace27061 100644
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -45,6 +45,7 @@ extern int	hw_ibrs_disable;
 extern int	hw_ssb_disable;
 extern int	nmi_flush_l1d_sw;
 extern int	syscall_ret_l1d_flush_mode;
+extern int	lass_enabled;
 
 extern vm_paddr_t intel_graphics_stolen_base;
 extern vm_paddr_t intel_graphics_stolen_size;