+ x86-xen-use-lazy_mmu_state-when-context-switching.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: x86/xen: use lazy_mmu_state when context-switching
has been added to the -mm mm-new branch.  Its filename is
     x86-xen-use-lazy_mmu_state-when-context-switching.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-xen-use-lazy_mmu_state-when-context-switching.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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------------------------------------------------------
From: Kevin Brodsky <kevin.brodsky@arm.com>
Subject: x86/xen: use lazy_mmu_state when context-switching
Date: Mon, 15 Dec 2025 15:03:22 +0000

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.

Link: https://lkml.kernel.org/r/20251215150323.2218608-14-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/include/asm/thread_info.h |    4 +---
 arch/x86/xen/enlighten_pv.c        |    3 +--
 2 files changed, 2 insertions(+), 5 deletions(-)

--- a/arch/x86/include/asm/thread_info.h~x86-xen-use-lazy_mmu_state-when-context-switching
+++ a/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() */
--- a/arch/x86/xen/enlighten_pv.c~x86-xen-use-lazy_mmu_state-when-context-switching
+++ a/arch/x86/xen/enlighten_pv.c
@@ -426,7 +426,6 @@ static void xen_start_context_switch(str
 
 	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(struc
 
 	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();
 }
 
_

Patches currently in -mm which might be from kevin.brodsky@arm.com are

x86-xen-simplify-flush_lazy_mmu.patch
powerpc-mm-implement-arch_flush_lazy_mmu_mode.patch
sparc-mm-implement-arch_flush_lazy_mmu_mode.patch
mm-clarify-lazy_mmu-sleeping-constraints.patch
mm-introduce-config_arch_has_lazy_mmu_mode.patch
mm-introduce-generic-lazy_mmu-helpers.patch
mm-bail-out-of-lazy_mmu_mode_-in-interrupt-context.patch
mm-enable-lazy_mmu-sections-to-nest.patch
arm64-mm-replace-tif_lazy_mmu-with-is_lazy_mmu_mode_active.patch
powerpc-mm-replace-batch-active-with-is_lazy_mmu_mode_active.patch
sparc-mm-replace-batch-active-with-is_lazy_mmu_mode_active.patch
x86-xen-use-lazy_mmu_state-when-context-switching.patch
mm-add-basic-tests-for-lazy_mmu.patch