Wolfgang Mauerer wrote:
> Jan Kiszka wrote:
>> If we enter __ipipe_handle_exception over a non-root domain and leave it
>> due to migration in the event handler over root, we must not restore the
>> root domain state so far saved on entry. This caused subtle pipeline
>> state corruptions. Instead, only save and restore them if we were
>> entering over root.
>>
>> However, the x86-32 regs.flags fixup is required nevertheless to take
>> care of mismatches between the root domain state and the hardware flags
>> on entry. That may happen if we fault in the iret path. But also in this
>> case we must not restore an invalid root domain state. So if we entered
>> over non-root, pick up the input for __fixup_if from the root domain
>> after running the ipipe handler.
>>
>> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
>> ---
>>
>> Next try. But this time I think I finally understood what scenario
>> __fixup_if is actually fixing. Please correct me if I'm still missing
>> one.
>
> looks good - it works for my test cases and solves the problems with
> the hw/pipeline state mismatch during early bootup. But do you happen
> to have any scenario at hand with ipipe_domain_root_p && !root_entry?
> Couldn't trigger this one yet so only the raw_irqs_disabled_flags
> fixup is excercised, though I guess it can't do any harm to really
> ensure that the explanation fits reality this time...
You mean non-root entry -> migration -> __fixup_if? In that case we pick
up the flags for fixup _after_ the migration (raw_irqs_disabled()). Or
what do you mean?
>
> Wolfgang
>
>> arch/x86/kernel/ipipe.c | 81
>> +++++++++++++++++++++++++++++-----------------
>> 1 files changed, 51 insertions(+), 30 deletions(-)
>>
>> diff --git a/arch/x86/kernel/ipipe.c b/arch/x86/kernel/ipipe.c
>> index 4442d96..b471355 100644
>> --- a/arch/x86/kernel/ipipe.c
>> +++ b/arch/x86/kernel/ipipe.c
>> @@ -702,19 +702,23 @@ static int __ipipe_xlate_signo[] = {
>>
>> int __ipipe_handle_exception(struct pt_regs *regs, long error_code, int
>> vector)
>> {
>> - unsigned long flags;
>> -
>> - /* Pick up the root domain state of the interrupted context. */
>> - local_save_flags(flags);
>> + bool root_entry = false;
>> + unsigned long flags = 0;
>>
>> if (ipipe_root_domain_p) {
>> - /*
>> - * Replicate hw interrupt state into the virtual mask before
>> - * calling the I-pipe event handler over the root domain. Also
>> - * required later when calling the Linux exception handler.
>> - */
>> - if (irqs_disabled_hw())
>> + root_entry = true;
>> +
>> + local_save_flags(flags);
>> +
>> + if (irqs_disabled_hw()) {
>> + /*
>> + * Replicate hw interrupt state into the virtual mask
>> + * before calling the I-pipe event handler over the
>> + * root domain. Also required later when calling the
>> + * Linux exception handler.
>> + */
>> local_irq_disable();
>> + }
>> }
>> #ifdef CONFIG_KGDB
>> /* catch exception KGDB is interested in over non-root domains */
>> @@ -725,18 +729,22 @@ int __ipipe_handle_exception(struct pt_regs *regs,
>> long error_code, int vector)
>> #endif /* CONFIG_KGDB */
>>
>> if (unlikely(ipipe_trap_notify(vector, regs))) {
>> - local_irq_restore_nosync(flags);
>> + if (root_entry)
>> + local_irq_restore_nosync(flags);
>> return 1;
>> }
>>
>> - /*
>> - * 32-bit: In case we migrated to root domain inside the event
>> - * handler, restore the original IF from exception entry as the
>> - * low-level return code will evaluate it.
>> - */
>> - __fixup_if(raw_irqs_disabled_flags(flags), regs);
>> -
>> - if (unlikely(!ipipe_root_domain_p)) {
>> + if (likely(ipipe_root_domain_p)) {
>> + /*
>> + * 32-bit: In case we faulted in the iret path, regs.flags do
>> + * not match the root domain state as the low-level return
>> + * code will evaluate it. Fix this up, either by the root
>> + * state sampled on entry or, if we migrated to root, with the
>> + * current state.
>> + */
>> + __fixup_if(root_entry ? raw_irqs_disabled_flags(flags) :
>> + raw_irqs_disabled(), regs);
>> + } else {
>> /* Detect unhandled faults over non-root domains. */
>> struct ipipe_domain *ipd = ipipe_current_domain;
>>
>> @@ -770,21 +778,29 @@ int __ipipe_handle_exception(struct pt_regs *regs,
>> long error_code, int vector)
>> * Relevant for 64-bit: Restore root domain state as the low-level
>> * return code will not align it to regs.flags.
>> */
>> - local_irq_restore_nosync(flags);
>> + if (root_entry)
>> + local_irq_restore_nosync(flags);
>>
>> return 0;
>> }
>>
>> int __ipipe_divert_exception(struct pt_regs *regs, int vector)
>> {
>> - unsigned long flags;
>> -
>> - /* Same root state handling as in __ipipe_handle_exception. */
>> - local_save_flags(flags);
>> + bool root_entry = false;
>> + unsigned long flags = 0;
>>
>> if (ipipe_root_domain_p) {
>> - if (irqs_disabled_hw())
>> + root_entry = true;
>> +
>> + local_save_flags(flags);
>> +
>> + if (irqs_disabled_hw()) {
>> + /*
>> + * Same root state handling as in
>> + * __ipipe_handle_exception.
>> + */
>> local_irq_disable();
>> + }
>> }
>> #ifdef CONFIG_KGDB
>> /* catch int1 and int3 over non-root domains */
>> @@ -804,16 +820,21 @@ int __ipipe_divert_exception(struct pt_regs *regs, int
>> vector)
>> #endif /* CONFIG_KGDB */
>>
>> if (unlikely(ipipe_trap_notify(vector, regs))) {
>> - local_irq_restore_nosync(flags);
>> + if (root_entry)
>> + local_irq_restore_nosync(flags);
>> return 1;
>> }
>>
>> + if (likely(ipipe_root_domain_p)) {
>> + /* see __ipipe_handle_exception */
>> + __fixup_if(root_entry ? raw_irqs_disabled_flags(flags) :
>> + raw_irqs_disabled(), regs);
>> + }
>> +
>> /*
>> - * 32-bit: Due to possible migration inside the event handler, we have
>> - * to restore IF so that low-level return code sets the root domain
>> - * state correctly.
>> + * No need to restore root state in the 64-bit case, the Linux handler
>> + * and the return code will take care of it.
>> */
>> - __fixup_if(raw_irqs_disabled_flags(flags), regs);
>>
>> return 0;
>> }
>
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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