From 7f9958230d8a79d474829bee25ec9426397335ce Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 30 Apr 2025 10:11:54 +0200 Subject: x86/mm: Fix false positive warning in switch_mm_irqs_off() Multiple testers reported the following new warning: WARNING: CPU: 0 PID: 0 at arch/x86/mm/tlb.c:795 Which corresponds to: if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(prev != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next)); So the problem is that unuse_temporary_mm() explicitly clears that bit; and it has to, because otherwise the flush_tlb_mm_range() in __text_poke() will try sending IPIs, which are not at all needed. See also: https://lore.kernel.org/all/20241113095550.GBZzR3pg-RhJKPDazS@fat_crate.local/ Notably, the whole {,un}use_temporary_mm() thing requires preemption to be disabled across it with the express purpose of keeping all TLB nonsense CPU local, such that invalidations can also stay local etc. However, as a side-effect, we violate this above WARN(), which sorta makes sense for the normal case, but very much doesn't make sense here. Change unuse_temporary_mm() to mark the mm_struct such that a further exception (beyond init_mm) can be grafted, to keep the warning for all the other cases. Reported-by: Chaitanya Kumar Borah Reported-by: Jani Nikula Signed-off-by: Peter Zijlstra Signed-off-by: Ingo Molnar Cc: Andrew Cooper Cc: Andy Lutomirski Cc: Brian Gerst Cc: H. Peter Anvin Cc: Juergen Gross Cc: Linus Torvalds Cc: Rik van Riel Link: https://lore.kernel.org/r/20250430081154.GH4439@noisy.programming.kicks-ass.net --- arch/x86/include/asm/mmu.h | 4 ++-- arch/x86/include/asm/mmu_context.h | 10 ++++++++++ arch/x86/mm/init.c | 3 +++ arch/x86/mm/tlb.c | 3 ++- arch/x86/platform/efi/efi_64.c | 1 + 5 files changed, 18 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h index 8b8055a8eb9e..0fe9c569d171 100644 --- a/arch/x86/include/asm/mmu.h +++ b/arch/x86/include/asm/mmu.h @@ -16,6 +16,8 @@ #define MM_CONTEXT_LOCK_LAM 2 /* Allow LAM and SVA coexisting */ #define MM_CONTEXT_FORCE_TAGGED_SVA 3 +/* Tracks mm_cpumask */ +#define MM_CONTEXT_NOTRACK 4 /* * x86 has arch-specific MMU state beyond what lives in mm_struct. @@ -44,9 +46,7 @@ typedef struct { struct ldt_struct *ldt; #endif -#ifdef CONFIG_X86_64 unsigned long flags; -#endif #ifdef CONFIG_ADDRESS_MASKING /* Active LAM mode: X86_CR3_LAM_U48 or X86_CR3_LAM_U57 or 0 (disabled) */ diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index c511f8584ae4..73bf3b1b44e8 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -247,6 +247,16 @@ static inline bool is_64bit_mm(struct mm_struct *mm) } #endif +static inline bool is_notrack_mm(struct mm_struct *mm) +{ + return test_bit(MM_CONTEXT_NOTRACK, &mm->context.flags); +} + +static inline void set_notrack_mm(struct mm_struct *mm) +{ + set_bit(MM_CONTEXT_NOTRACK, &mm->context.flags); +} + /* * We only want to enforce protection keys on the current process * because we effectively have no access to PKRU for other diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index f8c74d19bebb..aa56d9ac0b8f 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -28,6 +28,7 @@ #include #include #include +#include /* * We need to define the tracepoints somewhere, and tlb.c @@ -830,6 +831,8 @@ void __init poking_init(void) /* Xen PV guests need the PGD to be pinned. */ paravirt_enter_mmap(text_poke_mm); + set_notrack_mm(text_poke_mm); + /* * Randomize the poking address, but make sure that the following page * will be mapped at the same PMD. We need 2 pages, so find space for 3, diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 39761c7765bd..f5b990e46d7b 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -847,7 +847,8 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, * mm_cpumask. The TLB shootdown code can figure out from * cpu_tlbstate_shared.is_lazy whether or not to send an IPI. */ - if (IS_ENABLED(CONFIG_DEBUG_VM) && WARN_ON_ONCE(prev != &init_mm && + if (IS_ENABLED(CONFIG_DEBUG_VM) && + WARN_ON_ONCE(prev != &init_mm && !is_notrack_mm(prev) && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next)); diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index a5d3496d32a5..ce4c08adca88 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -89,6 +89,7 @@ int __init efi_alloc_page_tables(void) efi_mm.pgd = efi_pgd; mm_init_cpumask(&efi_mm); init_new_context(NULL, &efi_mm); + set_notrack_mm(&efi_mm); return 0; -- cgit v1.2.3