linux-kernel - [PATCH v7 02/12] x86/tlb: export flush_tlb_kernel

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Message-ID: <20250924151101.2225820-3-patrick.roy@campus.lmu.de>
Date: Wed, 24 Sep 2025 16:10:42 +0100
From: Patrick Roy <patrick.roy@...pus.lmu.de>
To: 
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Subject: [PATCH v7 02/12] x86/tlb: export flush_tlb_kernel_range to KVM module

From: Patrick Roy <roypat@...zon.co.uk>

After direct map removal, a TLB flush can be done to ensure that the
just-unmapped memory cannot be accessed through stale TLB entries. This
is particularly useful on modern hardware, where one can not rely on
timely TLB-eviction to ensure these entries go away.

This export is only needed on x86, as arm64 (the only other architecture
supporting guest_memfd currently) does not allow building KVM as a
module.

Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Patrick Roy <roypat@...zon.co.uk>
---
 arch/x86/include/asm/tlbflush.h | 3 ++-
 arch/x86/mm/tlb.c               | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 00daedfefc1b..6f57f7eb621b 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -317,7 +317,6 @@ extern void flush_tlb_all(void);
 extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 				unsigned long end, unsigned int stride_shift,
 				bool freed_tables);
-extern void flush_tlb_kernel_range(unsigned long start, unsigned long end);
 
 static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a)
 {
@@ -483,6 +482,8 @@ static inline void cpu_tlbstate_update_lam(unsigned long lam, u64 untag_mask)
 #endif
 #endif /* !MODULE */
 
+extern void flush_tlb_kernel_range(unsigned long start, unsigned long end);
+
 static inline void __native_tlb_flush_global(unsigned long cr4)
 {
 	native_write_cr4(cr4 ^ X86_CR4_PGE);
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 39f80111e6f1..dee5018bceeb 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1541,6 +1541,7 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
 
 	put_flush_tlb_info();
 }
+EXPORT_SYMBOL_FOR_MODULES(flush_tlb_kernel_range, "kvm");
 
 /*
  * This can be used from process context to figure out what the value of
-- 
2.51.0