[PATCH v6 13/14] x86/xen: use lazy_mmu_state when context-switching

Kevin Brodsky
2025-12-15T15:04:51Z

We currently set a TIF flag when scheduling out a task that is in
lazy MMU mode, in order to restore it when the task is scheduled
again.

The generic lazy_mmu layer now tracks whether a task is in lazy MMU
mode in task_struct::lazy_mmu_state. We can therefore check that
state when switching to the new task, instead of using a separate
TIF flag.

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
arch/x86/include/asm/thread_info.h | 4 +---
arch/x86/xen/enlighten_pv.c | 3 +--
2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e71e0e8362ed..0067684afb5b 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -100,8 +100,7 @@ struct thread_info {
#define TIF_FORCED_TF 24 /* true if TF in eflags artificially */
#define TIF_SINGLESTEP 25 /* reenable singlestep on user return*/
#define TIF_BLOCKSTEP 26 /* set when we want DEBUGCTLMSR_BTF */
-#define TIF_LAZY_MMU_UPDATES 27 /* task is updating the mmu lazily */
-#define TIF_ADDR32 28 /* 32-bit address space on 64 bits */
+#define TIF_ADDR32 27 /* 32-bit address space on 64 bits */

#define _TIF_SSBD BIT(TIF_SSBD)
#define _TIF_SPEC_IB BIT(TIF_SPEC_IB)
@@ -114,7 +113,6 @@ struct thread_info {
#define _TIF_FORCED_TF BIT(TIF_FORCED_TF)
#define _TIF_BLOCKSTEP BIT(TIF_BLOCKSTEP)
#define _TIF_SINGLESTEP BIT(TIF_SINGLESTEP)
-#define _TIF_LAZY_MMU_UPDATES BIT(TIF_LAZY_MMU_UPDATES)
#define _TIF_ADDR32 BIT(TIF_ADDR32)

/* flags to check in __switch_to() */
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4806cc28d7ca..98dbb6a61087 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -426,7 +426,6 @@ static void xen_start_context_switch(struct task_struct *prev)

if (this_cpu_read(xen_lazy_mode) == XEN_LAZY_MMU) {
arch_leave_lazy_mmu_mode();
- set_ti_thread_flag(task_thread_info(prev), TIF_LAZY_MMU_UPDATES);
}
enter_lazy(XEN_LAZY_CPU);
}
@@ -437,7 +436,7 @@ static void xen_end_context_switch(struct task_struct *next)

xen_mc_flush();
leave_lazy(XEN_LAZY_CPU);
- if (test_and_clear_ti_thread_flag(task_thread_info(next), TIF_LAZY_MMU_UPDATES))
+ if (__task_lazy_mmu_mode_active(next))
arch_enter_lazy_mmu_mode();
}

--
2.51.2