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SubjectRe: [PATCH v3 10/10] x86/split_lock: Handle #AC exception for split lock

* Fenghua Yu <fenghua.yu@intel.com> wrote:

> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -61,6 +61,7 @@
> #include <asm/mpx.h>
> #include <asm/vm86.h>
> #include <asm/umip.h>
> +#include <asm/cpu.h>
>
> #ifdef CONFIG_X86_64
> #include <asm/x86_init.h>
> @@ -292,9 +293,36 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, 0, NULL, "coprocessor segment overru
> DO_ERROR(X86_TRAP_TS, SIGSEGV, 0, NULL, "invalid TSS", invalid_TSS)
> DO_ERROR(X86_TRAP_NP, SIGBUS, 0, NULL, "segment not present", segment_not_present)
> DO_ERROR(X86_TRAP_SS, SIGBUS, 0, NULL, "stack segment", stack_segment)
> -DO_ERROR(X86_TRAP_AC, SIGBUS, BUS_ADRALN, NULL, "alignment check", alignment_check)
> #undef IP
>
> +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
> +{
> + unsigned int trapnr = X86_TRAP_AC;
> + char str[] = "alignment check";
> + int signr = SIGBUS;
> + int ret;
> +
> + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
> + NOTIFY_STOP) {
> + /* #AC exception could be handled by split lock handler. */
> + ret = do_ac_split_lock(regs);
> + if (ret) {
> + cond_local_irq_enable(regs);
> +
> + return;
> + }
> +
> + cond_local_irq_enable(regs);
> + /*
> + * If not processed by split lock handler, go to generic
> + * #AC handler.
> + */
> + do_trap(trapnr, signr, str, regs, error_code, BUS_ADRALN, NULL);
> + }
> +}

Is there any experience with how frequently this signal is killing
user-space processes on a modern distro? Any expectation of how frequent
such SIGBUS task terminations are going to be in the field?

Thanks,

Ingo

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