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    Subject[PATCH 1/2] x86/mce: Only restart instruction after machine check recovery if it is safe
    Section 15.3.1.2 of the software developer manual has this to say about the
    RIPV bit in the IA32_MCG_STATUS register:

    RIPV (restart IP valid) flag, bit 0 — Indicates (when set) that program
    execution can be restarted reliably at the instruction pointed to by the
    instruction pointer pushed on the stack when the machine-check exception
    is generated. When clear, the program cannot be reliably restarted at
    the pushed instruction pointer.

    We need to save the state of this bit in do_machine_check() and use it
    in mce_notify_process() to force a signal; even if memory_failure() says
    it made a complete recovery ... e.g. replaced a clean LRU page).

    Signed-off-by: Tony Luck <tony.luck@intel.com>
    ---
    arch/x86/kernel/cpu/mcheck/mce.c | 9 ++++++---
    1 files changed, 6 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
    index 66e1c51..3b8ebdc 100644
    --- a/arch/x86/kernel/cpu/mcheck/mce.c
    +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    @@ -947,9 +947,10 @@ struct mce_info {
    atomic_t inuse;
    struct task_struct *t;
    __u64 paddr;
    + int restartable;
    } mce_info[MCE_INFO_MAX];

    -static void mce_save_info(__u64 addr)
    +static void mce_save_info(__u64 addr, int c)
    {
    struct mce_info *mi;

    @@ -957,6 +958,7 @@ static void mce_save_info(__u64 addr)
    if (atomic_cmpxchg(&mi->inuse, 0, 1) == 0) {
    mi->t = current;
    mi->paddr = addr;
    + mi->restartable = c;
    return;
    }
    }
    @@ -1136,7 +1138,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
    mce_panic("Fatal machine check on current CPU", &m, msg);
    if (worst == MCE_AR_SEVERITY) {
    /* schedule action before return to userland */
    - mce_save_info(m.addr);
    + mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV);
    set_thread_flag(TIF_MCE_NOTIFY);
    } else if (kill_it) {
    force_sig(SIGBUS, current);
    @@ -1185,7 +1187,8 @@ void mce_notify_process(void)

    pr_err("Uncorrected hardware memory error in user-access at %llx",
    mi->paddr);
    - if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0) {
    + if (memory_failure(pfn, MCE_VECTOR, MF_ACTION_REQUIRED) < 0 ||
    + mi->restartable == 0) {
    pr_err("Memory error not recovered");
    force_sig(SIGBUS, current);
    }
    --
    1.7.9.rc2.1.g69204
    --
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