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    Subject[PATCH v2 7/8] x86/speculation: Use Indirect Branch Prediction Barrier in context switch
    Date
    From: Thomas Gleixner <tglx@linutronix.de>

    [peterz: comment]

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
    ---
    arch/x86/mm/tlb.c | 10 +++++++++-
    1 file changed, 9 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
    index a156195..304de7d 100644
    --- a/arch/x86/mm/tlb.c
    +++ b/arch/x86/mm/tlb.c
    @@ -6,13 +6,14 @@
    #include <linux/interrupt.h>
    #include <linux/export.h>
    #include <linux/cpu.h>
    +#include <linux/debugfs.h>

    #include <asm/tlbflush.h>
    #include <asm/mmu_context.h>
    +#include <asm/nospec-branch.h>
    #include <asm/cache.h>
    #include <asm/apic.h>
    #include <asm/uv/uv.h>
    -#include <linux/debugfs.h>

    /*
    * TLB flushing, formerly SMP-only
    @@ -220,6 +221,13 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
    u16 new_asid;
    bool need_flush;

    + /*
    + * Avoid user/user BTB poisoning by flushing the branch predictor
    + * when switching between processes. This stops one process from
    + * doing Spectre-v2 attacks on another.
    + */
    + indirect_branch_prediction_barrier();
    +
    if (IS_ENABLED(CONFIG_VMAP_STACK)) {
    /*
    * If our current stack is in vmalloc space and isn't
    --
    2.7.4
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