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Clearing the cpu in prev's mm_cpumask early will avoid the flush tlb
IPI's while the cr3 is still pointing to the prev mm. And this window
can lead to the possibility of bogus TLB fills resulting in strange
failures. One such problematic scenario is mentioned below.
T1. CPU-1 is context switching from mm1 to mm2 context and got a NMI
etc between the point of clearing the cpu from the mm_cpumask(mm1)
and before reloading the cr3 with the new mm2.
T2. CPU-2 is tearing down a specific vma for mm1 and will proceed with
flushing the TLB for mm1. It doesn't send the flush TLB to CPU-1
as it doesn't see that cpu listed in the mm_cpumask(mm1).
T3. After the TLB flush is complete, CPU-2 goes ahead and frees the
page-table pages associated with the removed vma mapping.
T4. CPU-2 now allocates those freed page-table pages for something
else.
T5. As the CR3 and TLB caches for mm1 is still active on CPU-1, CPU-1
can potentially speculate and walk through the page-table caches
and can insert new TLB entries. As the page-table pages are
already freed and being used on CPU-2, this page walk can
potentially insert a bogus global TLB entry depending on the
(random) contents of the page that is being used on CPU-2.
T6. This bogus TLB entry being global will be active across future CR3
changes and can result in weird memory corruption etc.
To avoid this issue, for the prev mm that is handing over the cpu to
another mm, clear the cpu from the mm_cpumask(prev) after the cr3 is
changed.
Marking it for -stable, though we haven't seen any reported failure that
can be attributed to this.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: stable@kernel.org [v2.6.32+]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
94 lines
2.1 KiB
C
94 lines
2.1 KiB
C
#ifndef _ASM_X86_MMU_CONTEXT_H
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#define _ASM_X86_MMU_CONTEXT_H
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#include <asm/desc.h>
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#include <asm/atomic.h>
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#include <asm/pgalloc.h>
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#include <asm/tlbflush.h>
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#include <asm/paravirt.h>
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#ifndef CONFIG_PARAVIRT
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#include <asm-generic/mm_hooks.h>
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static inline void paravirt_activate_mm(struct mm_struct *prev,
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struct mm_struct *next)
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{
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}
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#endif /* !CONFIG_PARAVIRT */
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/*
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* Used for LDT copy/destruction.
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*/
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int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
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void destroy_context(struct mm_struct *mm);
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static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
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{
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#ifdef CONFIG_SMP
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if (percpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
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percpu_write(cpu_tlbstate.state, TLBSTATE_LAZY);
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#endif
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}
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static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
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struct task_struct *tsk)
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{
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unsigned cpu = smp_processor_id();
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if (likely(prev != next)) {
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#ifdef CONFIG_SMP
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percpu_write(cpu_tlbstate.state, TLBSTATE_OK);
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percpu_write(cpu_tlbstate.active_mm, next);
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#endif
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cpumask_set_cpu(cpu, mm_cpumask(next));
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/* Re-load page tables */
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load_cr3(next->pgd);
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/* stop flush ipis for the previous mm */
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cpumask_clear_cpu(cpu, mm_cpumask(prev));
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/*
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* load the LDT, if the LDT is different:
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*/
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if (unlikely(prev->context.ldt != next->context.ldt))
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load_LDT_nolock(&next->context);
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}
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#ifdef CONFIG_SMP
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else {
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percpu_write(cpu_tlbstate.state, TLBSTATE_OK);
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BUG_ON(percpu_read(cpu_tlbstate.active_mm) != next);
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if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next))) {
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/* We were in lazy tlb mode and leave_mm disabled
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* tlb flush IPI delivery. We must reload CR3
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* to make sure to use no freed page tables.
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*/
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load_cr3(next->pgd);
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load_LDT_nolock(&next->context);
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}
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}
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#endif
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}
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#define activate_mm(prev, next) \
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do { \
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paravirt_activate_mm((prev), (next)); \
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switch_mm((prev), (next), NULL); \
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} while (0);
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#ifdef CONFIG_X86_32
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#define deactivate_mm(tsk, mm) \
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do { \
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lazy_load_gs(0); \
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} while (0)
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#else
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#define deactivate_mm(tsk, mm) \
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do { \
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load_gs_index(0); \
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loadsegment(fs, 0); \
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} while (0)
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#endif
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#endif /* _ASM_X86_MMU_CONTEXT_H */
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