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Date: Mon, 28 Sep 2009 15:40:23 +0900
From: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To: Huang Ying <ying.huang@...el.com>
CC: Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
Andi Kleen <ak@...ux.intel.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [BUGFIX -v2] x86, mce, inject: Make injected mce valid only during
faked handler call
Hi Huang,
Huang Ying wrote:
> In the current implementation, injected MCE is valid from the point
> the MCE is injected to the point the MCE is processed by the faked
> handler call.
>
> This has an undesired side-effect: it is possible for it to be
> consumed by real machine_check_poll. This may confuse a real system
> error and may confuse the mce test suite.
>
> To fix this, this patch introduces another flag MCJ_VALID to indicate
^^^^^^^^^
MCJ_LOADED?
> that the MCE entry is valid for injector but not for the
> handler. Another flag, mce.finished is used to indicate the MCE entry
> is valid for the handler.
>
> mce.finished is enabled only during faked MCE handler call and
> protected by IRQ disabling. This make it impossible for real
> machine_check_poll to consume it.
Are there the reverse case - is it possible that the faked handler
call might consume real error which is not handled yet by the real
machine_check_poll?
>
> Signed-off-by: Huang Ying <ying.huang@...el.com>
>
> v2:
> - Revise commit changelog (Thanks Ingo)
> - Change naming (XX_BIT for bit definition)
>
> ---
> arch/x86/include/asm/mce.h | 17 +++++++++++------
> arch/x86/kernel/cpu/mcheck/mce-inject.c | 23 ++++++++++++++++-------
> 2 files changed, 27 insertions(+), 13 deletions(-)
>
> --- a/arch/x86/include/asm/mce.h
> +++ b/arch/x86/include/asm/mce.h
> @@ -38,13 +38,18 @@
> #define MCM_ADDR_MEM 3 /* memory address */
> #define MCM_ADDR_GENERIC 7 /* generic */
>
> -#define MCJ_CTX_MASK 3
> +#define MCJ_NMI_BROADCAST_BIT 2 /* do NMI broadcasting */
> +#define MCJ_EXCEPTION_BIT 3 /* raise as exception */
> +#define MCJ_LOADED_BIT 4 /* entry is valid for injector */
> +
> +#define MCJ_CTX_MASK 0x03
> #define MCJ_CTX(flags) ((flags) & MCJ_CTX_MASK)
> -#define MCJ_CTX_RANDOM 0 /* inject context: random */
> -#define MCJ_CTX_PROCESS 1 /* inject context: process */
> -#define MCJ_CTX_IRQ 2 /* inject context: IRQ */
> -#define MCJ_NMI_BROADCAST 4 /* do NMI broadcasting */
> -#define MCJ_EXCEPTION 8 /* raise as exception */
> +#define MCJ_CTX_RANDOM 0x00 /* inject context: random */
> +#define MCJ_CTX_PROCESS 0x01 /* inject context: process */
> +#define MCJ_CTX_IRQ 0x02 /* inject context: IRQ */
> +#define MCJ_NMI_BROADCAST (1 << MCJ_NMI_BROADCAST_BIT)
> +#define MCJ_EXCEPTION (1 << MCJ_EXCEPTION_BIT)
> +#define MCJ_LOADED (1 << MCJ_LOADED_BIT)
I'd like to see a patch to replace MCJ_* to MCE_INJ_* before
adding new flag.
>
> /* Fields are zero when not available */
> struct mce {
> --- a/arch/x86/kernel/cpu/mcheck/mce-inject.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce-inject.c
> @@ -32,16 +32,16 @@ static void inject_mce(struct mce *m)
>
> /* Make sure noone reads partially written injectm */
> i->finished = 0;
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&i->inject_flags);
> mb();
> m->finished = 0;
> - /* First set the fields after finished */
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
> i->extcpu = m->extcpu;
> mb();
> - /* Now write record in order, finished last (except above) */
> memcpy(i, m, sizeof(struct mce));
> /* Finally activate it */
> mb();
> - i->finished = 1;
> + set_bit(MCJ_LOADED_BIT, (unsigned long *)&i->inject_flags);
Why
clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
set_bit(MCJ_LOADED_BIT, (unsigned long *)&i->inject_flags);
cannot be
m->inject_flags &= ~MCJ_LOADED;
m->inject_flags |= MCJ_LOADED;
?
If it can, defined *_BIT will not be necessary here.
> }
>
> static void raise_poll(struct mce *m)
> @@ -51,9 +51,11 @@ static void raise_poll(struct mce *m)
>
> memset(&b, 0xff, sizeof(mce_banks_t));
> local_irq_save(flags);
> + m->finished = 1;
> machine_check_poll(0, &b);
> - local_irq_restore(flags);
> m->finished = 0;
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
> + local_irq_restore(flags);
> }
I think the "finished" is not good name. (I suppose it is named
after "loading data to structure have been finished" or so.)
And also I think "MCJ_LOADED" is not good name, because I could not
figure out the difference between "loading finished" and "loaded."
OTOH in the course of nature mce_rdmsrl() returns injected data
anytime if data is loaded, because it is defined to do so.
304 /* MSR access wrappers used for error injection */
305 static u64 mce_rdmsrl(u32 msr)
306 {
307 u64 v;
308
309 if (__get_cpu_var(injectm).finished) {
I believe what you want to do here is "make mce_rdmsrl()/mce_wrmsrl()
to refer faked data only during faked handler call."
Then what we have to do is making a flag to indicate that "now
in faked handler call," for an example:
309 if (__get_cpu_var(mce_fake_in_progress)) {
and:
local_irq_save(flags);
__get_cpu_var(mce_fake_in_progress) = 1;
machine_check_poll(0, &b);
__get_cpu_var(mce_fake_in_progress) = 0;
local_irq_restore(flags);
>
> static void raise_exception(struct mce *m, struct pt_regs *pregs)
> @@ -69,9 +71,11 @@ static void raise_exception(struct mce *
> }
> /* in mcheck exeception handler, irq will be disabled */
> local_irq_save(flags);
> + m->finished = 1;
> do_machine_check(pregs, 0);
> - local_irq_restore(flags);
> m->finished = 0;
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
> + local_irq_restore(flags);
> }
>
> static cpumask_t mce_inject_cpumask;
> @@ -89,6 +93,8 @@ static int mce_raise_notify(struct notif
> raise_exception(m, args->regs);
> else if (m->status)
> raise_poll(m);
> + else
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
> return NOTIFY_STOP;
> }
>
> @@ -129,7 +135,7 @@ static int raise_local(void)
> mce_notify_irq();
> printk(KERN_INFO "Machine check poll done on CPU %d\n", cpu);
> } else
> - m->finished = 0;
> + clear_bit(MCJ_LOADED_BIT, (unsigned long *)&m->inject_flags);
>
> return ret;
> }
> @@ -152,10 +158,13 @@ static void raise_mce(struct mce *m)
> cpu_clear(get_cpu(), mce_inject_cpumask);
> for_each_online_cpu(cpu) {
> struct mce *mcpu = &per_cpu(injectm, cpu);
> - if (!mcpu->finished ||
> + if (!test_bit(MCJ_LOADED_BIT,
> + (unsigned long *)&mcpu->inject_flags) ||
> MCJ_CTX(mcpu->inject_flags) != MCJ_CTX_RANDOM)
> cpu_clear(cpu, mce_inject_cpumask);
> }
> + /* make sure needed data is available on other CPUs */
> + smp_mb();
What data are you taking care here for?
Thanks,
H.Seto
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