From 2d3a9dff763faa5b0182f3ea4e3f81d25bd1423c Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 6 Aug 2021 12:31:04 +0100 Subject: [PATCH] arm64: mm: Fix TLBI vs ASID rollover commit 5e10f9887ed85d4f59266d5c60dd09be96b5dbd4 upstream. When switching to an 'mm_struct' for the first time following an ASID rollover, a new ASID may be allocated and assigned to 'mm->context.id'. This reassignment can happen concurrently with other operations on the mm, such as unmapping pages and subsequently issuing TLB invalidation. Consequently, we need to ensure that (a) accesses to 'mm->context.id' are atomic and (b) all page-table updates made prior to a TLBI using the old ASID are guaranteed to be visible to CPUs running with the new ASID. This was found by inspection after reviewing the VMID changes from Shameer but it looks like a real (yet hard to hit) bug. Cc: Cc: Marc Zyngier Cc: Jade Alglave Cc: Shameer Kolothum Signed-off-by: Will Deacon Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20210806113109.2475-2-will@kernel.org Signed-off-by: Catalin Marinas Signed-off-by: Greg Kroah-Hartman --- arch/arm64/include/asm/mmu.h | 29 +++++++++++++++++++++++++---- arch/arm64/include/asm/tlbflush.h | 11 ++++++----- 2 files changed, 31 insertions(+), 9 deletions(-) diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h index b2e91c1..c731586 100644 --- a/arch/arm64/include/asm/mmu.h +++ b/arch/arm64/include/asm/mmu.h @@ -30,11 +30,32 @@ typedef struct { } mm_context_t; /* - * This macro is only used by the TLBI and low-level switch_mm() code, - * neither of which can race with an ASID change. We therefore don't - * need to reload the counter using atomic64_read(). + * We use atomic64_read() here because the ASID for an 'mm_struct' can + * be reallocated when scheduling one of its threads following a + * rollover event (see new_context() and flush_context()). In this case, + * a concurrent TLBI (e.g. via try_to_unmap_one() and ptep_clear_flush()) + * may use a stale ASID. This is fine in principle as the new ASID is + * guaranteed to be clean in the TLB, but the TLBI routines have to take + * care to handle the following race: + * + * CPU 0 CPU 1 CPU 2 + * + * // ptep_clear_flush(mm) + * xchg_relaxed(pte, 0) + * DSB ISHST + * old = ASID(mm) + * | + * | new = new_context(mm) + * \-----------------> atomic_set(mm->context.id, new) + * cpu_switch_mm(mm) + * // Hardware walk of pte using new ASID + * TLBI(old) + * + * In this scenario, the barrier on CPU 0 and the dependency on CPU 1 + * ensure that the page-table walker on CPU 1 *must* see the invalid PTE + * written by CPU 0. */ -#define ASID(mm) ((mm)->context.id.counter & 0xffff) +#define ASID(mm) (atomic64_read(&(mm)->context.id) & 0xffff) static inline bool arm64_kernel_unmapped_at_el0(void) { diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h index cc3f5a3..36f0289 100644 --- a/arch/arm64/include/asm/tlbflush.h +++ b/arch/arm64/include/asm/tlbflush.h @@ -245,9 +245,10 @@ static inline void flush_tlb_all(void) static inline void flush_tlb_mm(struct mm_struct *mm) { - unsigned long asid = __TLBI_VADDR(0, ASID(mm)); + unsigned long asid; dsb(ishst); + asid = __TLBI_VADDR(0, ASID(mm)); __tlbi(aside1is, asid); __tlbi_user(aside1is, asid); dsb(ish); @@ -256,9 +257,10 @@ static inline void flush_tlb_mm(struct mm_struct *mm) static inline void flush_tlb_page_nosync(struct vm_area_struct *vma, unsigned long uaddr) { - unsigned long addr = __TLBI_VADDR(uaddr, ASID(vma->vm_mm)); + unsigned long addr; dsb(ishst); + addr = __TLBI_VADDR(uaddr, ASID(vma->vm_mm)); __tlbi(vale1is, addr); __tlbi_user(vale1is, addr); } @@ -283,9 +285,7 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma, { int num = 0; int scale = 0; - unsigned long asid = ASID(vma->vm_mm); - unsigned long addr; - unsigned long pages; + unsigned long asid, addr, pages; start = round_down(start, stride); end = round_up(end, stride); @@ -305,6 +305,7 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma, } dsb(ishst); + asid = ASID(vma->vm_mm); /* * When the CPU does not support TLB range operations, flush the TLB -- 2.7.4