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Re: [PATCH 2/2] efi: implement interruptible runtime services

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  Re: [PATCH 2/2] efi: implement interruptible runtime services Matt Fleming <matt@codeblueprint.co.uk> - 2016-01-06 14:00 +0100
    Re: [PATCH 2/2] efi: implement interruptible runtime services Sylvain Chouleur <sylvain.chouleur@gmail.com> - 2016-01-06 17:00 +0100
      Re: [PATCH 2/2] efi: implement interruptible runtime services Matt Fleming <matt@codeblueprint.co.uk> - 2016-01-08 11:40 +0100
        Re: [PATCH 2/2] efi: implement interruptible runtime services Sylvain Chouleur <sylvain.chouleur@gmail.com> - 2016-01-08 15:00 +0100
          Re: [PATCH 2/2] efi: implement interruptible runtime services Matt Fleming <matt@codeblueprint.co.uk> - 2016-01-14 17:30 +0100

#1302737 — Re: [PATCH 2/2] efi: implement interruptible runtime services

On Fri, 18 Dec, at 11:29:51AM, sylvain.chouleur@gmail.com wrote:
> From: Sylvain Chouleur <sylvain.chouleur@intel.com>
> 
> This patch adds an implementation of EFI runtime services wappers which
> allow interrupts and preemption during execution of BIOS code.
> 
> It's needed by Broxton platform which requires the OS to do the write
> of the non volatile variables. To do that, the OS will receive an
> interrupt coming from the firmware to notify that it must write the
> data.
> 
> BIOS code must be executed using a specific PGD. This is currently
> done by efi_call() which force value of CR3 before calling BIOS and
> restore previous value after.
> 
> We use a dedicated kthread which will execute all interruptible runtime
> services. This efi_kthread is special because it has it's own mm_struct
> whereas kthread should not have one. This mm_struct contains the EFI PGD
> so the scheduler will load it before running any BIOS code.
> 
> Obviously, an interruptible runtime service must never be called from an
> interrupt context. EFI pstore is the only use case here, that's why we
> require it to be disabled when activating interruptible runtime services.
> 
> Signed-off-by: Sylvain Chouleur <sylvain.chouleur@intel.com>
> ---
>  arch/x86/Kconfig                          |  14 +++
>  arch/x86/include/asm/efi.h                |   1 +
>  arch/x86/platform/efi/Makefile            |   1 +
>  arch/x86/platform/efi/efi_32.c            |   5 +
>  arch/x86/platform/efi/efi_64.c            |   5 +
>  arch/x86/platform/efi/efi_interruptible.c | 191 ++++++++++++++++++++++++++++++
>  6 files changed, 217 insertions(+)
>  create mode 100644 arch/x86/platform/efi/efi_interruptible.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index db3622f22b61..3ddd5a9cab30 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1720,6 +1720,20 @@ config EFI_MIXED
>  
>  	   If unsure, say N.
>  
> +if X86_64
> +config EFI_INTERRUPTIBLE
> +	bool "Interruptible Efi Runtime Services"
> +	depends on EFI && !EFI_VARS_PSTORE
> +	default n
> +	help
> +          This is an interruptible implementation of efi runtime
> +	  services wrappers. If you say Y, BIOS code could be
> +	  interrupted and preempted as a standard process. Enable this
> +	  only if you are sure that your BIOS will support
> +	  interruptible efi calls
> +	  In doubt, say "N".
> +endif
> +

These words should be a little more assertive. Almost everyone is
going to want to turn this feature off.

> +static efi_status_t
> +non_blocking_not_allowed(__attribute__((unused)) efi_char16_t *name,
> +			 __attribute__((unused)) efi_guid_t *vendor,
> +			 __attribute__((unused)) u32 attr,
> +			 __attribute__((unused)) unsigned long data_size,
> +			 __attribute__((unused)) void *data)
> +{
> +	pr_err("efi_interruptible: non bloking operation is not allowed\n");
> +	return EFI_UNSUPPORTED;
> +}

Typo, s/bloking/blocking/

> +static int efi_interruptible_panic_notifier_call(
> +	struct notifier_block *notifier,
> +	unsigned long what, void *data)
> +{
> +	static struct efivars generic_efivars;
> +	static struct efivar_operations generic_ops;
> +
> +	generic_ops.get_variable = efi.get_variable;
> +	generic_ops.set_variable = efi.set_variable;
> +	generic_ops.get_next_variable = efi.get_next_variable;
> +	generic_ops.query_variable_store = efi_query_variable_store;
> +
> +	efivars_register(&generic_efivars, &generic_ops, efivars_kobject());
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block panic_nb = {
> +	.notifier_call = efi_interruptible_panic_notifier_call,
> +	.priority = 100,
> +};
> +

What's the purpose of this? The only reason you'd want to do this that
I can think of is because you'd want efi-pstore to run and attempt to
save some crash data for you. But you can't build with efi-pstore
enable and CONFIG_EFI_INTERRUPTIBLE.

I'd be tempted to just delete this notifier code.

> +static struct task_struct *efi_kworker_task;
> +static struct efivar_operations interruptible_ops;
> +static __init int efi_interruptible_init(void)
> +{
> +	int ret;
> +
> +	efi_kworker_task = kthread_create(kthread_worker_fn, &efi_kworker,
> +					  "efi_kthread");
> +	if (IS_ERR(efi_kworker_task)) {
> +		pr_err("efi_interruptible: Failed to create kthread\n");
> +		ret = PTR_ERR(efi_kworker_task);
> +		efi_kworker_task = NULL;
> +		return ret;
> +	}
> +
> +	efi_kworker_task->mm = mm_alloc();
> +	efi_kworker_task->active_mm = efi_kworker_task->mm;
> +	efi_kworker_task->mm->pgd = efi_get_pgd();
> +	wake_up_process(efi_kworker_task);
> +
> +	atomic_notifier_chain_register(&panic_notifier_list, &panic_nb);
> +
> +	interruptible_ops.get_variable = get_variable_interruptible;
> +	interruptible_ops.set_variable = set_variable_interruptible;
> +	interruptible_ops.set_variable_nonblocking = non_blocking_not_allowed;
> +	interruptible_ops.get_next_variable = get_next_variable_interruptible;
> +	interruptible_ops.query_variable_store = efi_query_variable_store;
> +	return efivars_register(&interruptible_efivars, &interruptible_ops,
> +				efivars_kobject());
> +}
> +

Is there some way we can match DMI/PCI identifiers for Broxton so that
we don't start seeing people accidentally running with preemptible EFI
services on non-BXT hardware?
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#1302866

2016-01-06 13:58 GMT+01:00 Matt Fleming <matt@codeblueprint.co.uk>:
> On Fri, 18 Dec, at 11:29:51AM, sylvain.chouleur@gmail.com wrote:
>> From: Sylvain Chouleur <sylvain.chouleur@intel.com>
>>
>> This patch adds an implementation of EFI runtime services wappers which
>> allow interrupts and preemption during execution of BIOS code.
>>
>> It's needed by Broxton platform which requires the OS to do the write
>> of the non volatile variables. To do that, the OS will receive an
>> interrupt coming from the firmware to notify that it must write the
>> data.
>>
>> BIOS code must be executed using a specific PGD. This is currently
>> done by efi_call() which force value of CR3 before calling BIOS and
>> restore previous value after.
>>
>> We use a dedicated kthread which will execute all interruptible runtime
>> services. This efi_kthread is special because it has it's own mm_struct
>> whereas kthread should not have one. This mm_struct contains the EFI PGD
>> so the scheduler will load it before running any BIOS code.
>>
>> Obviously, an interruptible runtime service must never be called from an
>> interrupt context. EFI pstore is the only use case here, that's why we
>> require it to be disabled when activating interruptible runtime services.
>>
>> Signed-off-by: Sylvain Chouleur <sylvain.chouleur@intel.com>
>> ---
>>  arch/x86/Kconfig                          |  14 +++
>>  arch/x86/include/asm/efi.h                |   1 +
>>  arch/x86/platform/efi/Makefile            |   1 +
>>  arch/x86/platform/efi/efi_32.c            |   5 +
>>  arch/x86/platform/efi/efi_64.c            |   5 +
>>  arch/x86/platform/efi/efi_interruptible.c | 191 ++++++++++++++++++++++++++++++
>>  6 files changed, 217 insertions(+)
>>  create mode 100644 arch/x86/platform/efi/efi_interruptible.c
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index db3622f22b61..3ddd5a9cab30 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1720,6 +1720,20 @@ config EFI_MIXED
>>
>>          If unsure, say N.
>>
>> +if X86_64
>> +config EFI_INTERRUPTIBLE
>> +     bool "Interruptible Efi Runtime Services"
>> +     depends on EFI && !EFI_VARS_PSTORE
>> +     default n
>> +     help
>> +          This is an interruptible implementation of efi runtime
>> +       services wrappers. If you say Y, BIOS code could be
>> +       interrupted and preempted as a standard process. Enable this
>> +       only if you are sure that your BIOS will support
>> +       interruptible efi calls
>> +       In doubt, say "N".
>> +endif
>> +
>
> These words should be a little more assertive. Almost everyone is
> going to want to turn this feature off.
>
>> +static efi_status_t
>> +non_blocking_not_allowed(__attribute__((unused)) efi_char16_t *name,
>> +                      __attribute__((unused)) efi_guid_t *vendor,
>> +                      __attribute__((unused)) u32 attr,
>> +                      __attribute__((unused)) unsigned long data_size,
>> +                      __attribute__((unused)) void *data)
>> +{
>> +     pr_err("efi_interruptible: non bloking operation is not allowed\n");
>> +     return EFI_UNSUPPORTED;
>> +}
>
> Typo, s/bloking/blocking/
>
>> +static int efi_interruptible_panic_notifier_call(
>> +     struct notifier_block *notifier,
>> +     unsigned long what, void *data)
>> +{
>> +     static struct efivars generic_efivars;
>> +     static struct efivar_operations generic_ops;
>> +
>> +     generic_ops.get_variable = efi.get_variable;
>> +     generic_ops.set_variable = efi.set_variable;
>> +     generic_ops.get_next_variable = efi.get_next_variable;
>> +     generic_ops.query_variable_store = efi_query_variable_store;
>> +
>> +     efivars_register(&generic_efivars, &generic_ops, efivars_kobject());
>> +
>> +     return NOTIFY_DONE;
>> +}
>> +
>> +static struct notifier_block panic_nb = {
>> +     .notifier_call = efi_interruptible_panic_notifier_call,
>> +     .priority = 100,
>> +};
>> +
>
> What's the purpose of this? The only reason you'd want to do this that
> I can think of is because you'd want efi-pstore to run and attempt to
> save some crash data for you. But you can't build with efi-pstore
> enable and CONFIG_EFI_INTERRUPTIBLE.
>
> I'd be tempted to just delete this notifier code.

This is indeed to be able to try write some crash data when we
are in a panic context.  In fact with this restoration of legacy
efi handlers on a panic we should be able to have pstore working
with CONFIG_EFI_INTERRUPTIBLE.

I say should because there is still issues with BIOS to have the
panic flow working.

>
>> +static struct task_struct *efi_kworker_task;
>> +static struct efivar_operations interruptible_ops;
>> +static __init int efi_interruptible_init(void)
>> +{
>> +     int ret;
>> +
>> +     efi_kworker_task = kthread_create(kthread_worker_fn, &efi_kworker,
>> +                                       "efi_kthread");
>> +     if (IS_ERR(efi_kworker_task)) {
>> +             pr_err("efi_interruptible: Failed to create kthread\n");
>> +             ret = PTR_ERR(efi_kworker_task);
>> +             efi_kworker_task = NULL;
>> +             return ret;
>> +     }
>> +
>> +     efi_kworker_task->mm = mm_alloc();
>> +     efi_kworker_task->active_mm = efi_kworker_task->mm;
>> +     efi_kworker_task->mm->pgd = efi_get_pgd();
>> +     wake_up_process(efi_kworker_task);
>> +
>> +     atomic_notifier_chain_register(&panic_notifier_list, &panic_nb);
>> +
>> +     interruptible_ops.get_variable = get_variable_interruptible;
>> +     interruptible_ops.set_variable = set_variable_interruptible;
>> +     interruptible_ops.set_variable_nonblocking = non_blocking_not_allowed;
>> +     interruptible_ops.get_next_variable = get_next_variable_interruptible;
>> +     interruptible_ops.query_variable_store = efi_query_variable_store;
>> +     return efivars_register(&interruptible_efivars, &interruptible_ops,
>> +                             efivars_kobject());
>> +}
>> +
>
> Is there some way we can match DMI/PCI identifiers for Broxton so that
> we don't start seeing people accidentally running with preemptible EFI
> services on non-BXT hardware?

I don't see how since this depends on a storage strategy more
than the SoC itself, it can be used on future platforms or we can
also get rid of it on BXT if an other storage is used for efi
variables.
Can't the KConfig protection be enough?

-- 
Sylvain
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#1304357

On Wed, 06 Jan, at 04:57:41PM, Sylvain Chouleur wrote:
> 2016-01-06 13:58 GMT+01:00 Matt Fleming <matt@codeblueprint.co.uk>:
> > On Fri, 18 Dec, at 11:29:51AM, sylvain.chouleur@gmail.com wrote:
> >> From: Sylvain Chouleur <sylvain.chouleur@intel.com>
> >>
> >> +static int efi_interruptible_panic_notifier_call(
> >> +     struct notifier_block *notifier,
> >> +     unsigned long what, void *data)
> >> +{
> >> +     static struct efivars generic_efivars;
> >> +     static struct efivar_operations generic_ops;
> >> +
> >> +     generic_ops.get_variable = efi.get_variable;
> >> +     generic_ops.set_variable = efi.set_variable;
> >> +     generic_ops.get_next_variable = efi.get_next_variable;
> >> +     generic_ops.query_variable_store = efi_query_variable_store;
> >> +
> >> +     efivars_register(&generic_efivars, &generic_ops, efivars_kobject());
> >> +
> >> +     return NOTIFY_DONE;
> >> +}
> >> +
> >> +static struct notifier_block panic_nb = {
> >> +     .notifier_call = efi_interruptible_panic_notifier_call,
> >> +     .priority = 100,
> >> +};
> >> +
> >
> > What's the purpose of this? The only reason you'd want to do this that
> > I can think of is because you'd want efi-pstore to run and attempt to
> > save some crash data for you. But you can't build with efi-pstore
> > enable and CONFIG_EFI_INTERRUPTIBLE.
> >
> > I'd be tempted to just delete this notifier code.
> 
> This is indeed to be able to try write some crash data when we
> are in a panic context.  In fact with this restoration of legacy
> efi handlers on a panic we should be able to have pstore working
> with CONFIG_EFI_INTERRUPTIBLE.
 
This makes the efivar registration more complicated because now it can
fail if someone else is holding efivars_lock. Which is a strange
semantic for a registration function.

> I say should because there is still issues with BIOS to have the
> panic flow working.

How would it work though? You'd need the kernel thread controlling
access to the flash to be run in order for any data to appear in the
EFI variable store. Except you're in the middle of a panic and all
bets are off regarding which tasks are going to be run by the
scheduler.

Until those issues are resolved, please delete the notifier code. But
honestly, I doubt this will ever be useful in practice. Setting up
panic handlers *once* you've crashed is far too late.

> >> +static struct task_struct *efi_kworker_task;
> >> +static struct efivar_operations interruptible_ops;
> >> +static __init int efi_interruptible_init(void)
> >> +{
> >> +     int ret;
> >> +
> >> +     efi_kworker_task = kthread_create(kthread_worker_fn, &efi_kworker,
> >> +                                       "efi_kthread");
> >> +     if (IS_ERR(efi_kworker_task)) {
> >> +             pr_err("efi_interruptible: Failed to create kthread\n");
> >> +             ret = PTR_ERR(efi_kworker_task);
> >> +             efi_kworker_task = NULL;
> >> +             return ret;
> >> +     }
> >> +
> >> +     efi_kworker_task->mm = mm_alloc();
> >> +     efi_kworker_task->active_mm = efi_kworker_task->mm;
> >> +     efi_kworker_task->mm->pgd = efi_get_pgd();
> >> +     wake_up_process(efi_kworker_task);
> >> +
> >> +     atomic_notifier_chain_register(&panic_notifier_list, &panic_nb);
> >> +
> >> +     interruptible_ops.get_variable = get_variable_interruptible;
> >> +     interruptible_ops.set_variable = set_variable_interruptible;
> >> +     interruptible_ops.set_variable_nonblocking = non_blocking_not_allowed;
> >> +     interruptible_ops.get_next_variable = get_next_variable_interruptible;
> >> +     interruptible_ops.query_variable_store = efi_query_variable_store;
> >> +     return efivars_register(&interruptible_efivars, &interruptible_ops,
> >> +                             efivars_kobject());
> >> +}
> >> +
> >
> > Is there some way we can match DMI/PCI identifiers for Broxton so that
> > we don't start seeing people accidentally running with preemptible EFI
> > services on non-BXT hardware?
> 
> I don't see how since this depends on a storage strategy more
> than the SoC itself, it can be used on future platforms or we can
> also get rid of it on BXT if an other storage is used for efi
> variables.
> Can't the KConfig protection be enough?

Kconfig is a last resort because it's a build-time decision and
greatly limits the flexibility of the kernel. It becomes no longer
possible to run a single kernel image with various CONFIG_* enabled on
x86 hardware - you now need a special EFI_INTERRUPTIBLE build.

Which apart from being a major headache for distributions in general
is generally frowned upon for the x86 architecture.

If there's any way at all of making this a runtime decision that would
be much better.

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#1304560

2016-01-08 11:38 GMT+01:00 Matt Fleming <matt@codeblueprint.co.uk>:
> On Wed, 06 Jan, at 04:57:41PM, Sylvain Chouleur wrote:
>> 2016-01-06 13:58 GMT+01:00 Matt Fleming <matt@codeblueprint.co.uk>:
>> > On Fri, 18 Dec, at 11:29:51AM, sylvain.chouleur@gmail.com wrote:
>> >> From: Sylvain Chouleur <sylvain.chouleur@intel.com>
>> >>
>> >> +static int efi_interruptible_panic_notifier_call(
>> >> +     struct notifier_block *notifier,
>> >> +     unsigned long what, void *data)
>> >> +{
>> >> +     static struct efivars generic_efivars;
>> >> +     static struct efivar_operations generic_ops;
>> >> +
>> >> +     generic_ops.get_variable = efi.get_variable;
>> >> +     generic_ops.set_variable = efi.set_variable;
>> >> +     generic_ops.get_next_variable = efi.get_next_variable;
>> >> +     generic_ops.query_variable_store = efi_query_variable_store;
>> >> +
>> >> +     efivars_register(&generic_efivars, &generic_ops, efivars_kobject());
>> >> +
>> >> +     return NOTIFY_DONE;
>> >> +}
>> >> +
>> >> +static struct notifier_block panic_nb = {
>> >> +     .notifier_call = efi_interruptible_panic_notifier_call,
>> >> +     .priority = 100,
>> >> +};
>> >> +
>> >
>> > What's the purpose of this? The only reason you'd want to do this that
>> > I can think of is because you'd want efi-pstore to run and attempt to
>> > save some crash data for you. But you can't build with efi-pstore
>> > enable and CONFIG_EFI_INTERRUPTIBLE.
>> >
>> > I'd be tempted to just delete this notifier code.
>>
>> This is indeed to be able to try write some crash data when we
>> are in a panic context.  In fact with this restoration of legacy
>> efi handlers on a panic we should be able to have pstore working
>> with CONFIG_EFI_INTERRUPTIBLE.
>
> This makes the efivar registration more complicated because now it can
> fail if someone else is holding efivars_lock. Which is a strange
> semantic for a registration function.

Right, I'll change the code to call legacy handlers from efi_interruptible code
directly it will be more consistent with a panic specific behavior.

>
>> I say should because there is still issues with BIOS to have the
>> panic flow working.
>
> How would it work though? You'd need the kernel thread controlling
> access to the flash to be run in order for any data to appear in the
> EFI variable store. Except you're in the middle of a panic and all
> bets are off regarding which tasks are going to be run by the
> scheduler.

The trick here is that in panic context, the cse is notified of this special
context and is asked to write data itself to the storage instead of sending
interrupt to the kernel. Then we don't need interruptible handler in
panic context. That's why we want to use legacy efi variable handlers.

>
> Until those issues are resolved, please delete the notifier code. But
> honestly, I doubt this will ever be useful in practice. Setting up
> panic handlers *once* you've crashed is far too late.

I understand, like I said above I'll modify efi_interruptible handlers to
call legacy ones in case of panic context.
I would like to avoid removing the panic part of this patch and take time
to clean it before merging the whole.

>
>> >> +static struct task_struct *efi_kworker_task;
>> >> +static struct efivar_operations interruptible_ops;
>> >> +static __init int efi_interruptible_init(void)
>> >> +{
>> >> +     int ret;
>> >> +
>> >> +     efi_kworker_task = kthread_create(kthread_worker_fn, &efi_kworker,
>> >> +                                       "efi_kthread");
>> >> +     if (IS_ERR(efi_kworker_task)) {
>> >> +             pr_err("efi_interruptible: Failed to create kthread\n");
>> >> +             ret = PTR_ERR(efi_kworker_task);
>> >> +             efi_kworker_task = NULL;
>> >> +             return ret;
>> >> +     }
>> >> +
>> >> +     efi_kworker_task->mm = mm_alloc();
>> >> +     efi_kworker_task->active_mm = efi_kworker_task->mm;
>> >> +     efi_kworker_task->mm->pgd = efi_get_pgd();
>> >> +     wake_up_process(efi_kworker_task);
>> >> +
>> >> +     atomic_notifier_chain_register(&panic_notifier_list, &panic_nb);
>> >> +
>> >> +     interruptible_ops.get_variable = get_variable_interruptible;
>> >> +     interruptible_ops.set_variable = set_variable_interruptible;
>> >> +     interruptible_ops.set_variable_nonblocking = non_blocking_not_allowed;
>> >> +     interruptible_ops.get_next_variable = get_next_variable_interruptible;
>> >> +     interruptible_ops.query_variable_store = efi_query_variable_store;
>> >> +     return efivars_register(&interruptible_efivars, &interruptible_ops,
>> >> +                             efivars_kobject());
>> >> +}
>> >> +
>> >
>> > Is there some way we can match DMI/PCI identifiers for Broxton so that
>> > we don't start seeing people accidentally running with preemptible EFI
>> > services on non-BXT hardware?
>>
>> I don't see how since this depends on a storage strategy more
>> than the SoC itself, it can be used on future platforms or we can
>> also get rid of it on BXT if an other storage is used for efi
>> variables.
>> Can't the KConfig protection be enough?
>
> Kconfig is a last resort because it's a build-time decision and
> greatly limits the flexibility of the kernel. It becomes no longer
> possible to run a single kernel image with various CONFIG_* enabled on
> x86 hardware - you now need a special EFI_INTERRUPTIBLE build.
>
> Which apart from being a major headache for distributions in general
> is generally frowned upon for the x86 architecture.
>
> If there's any way at all of making this a runtime decision that would
> be much better.

I think the best would be to bind this driver with the one which receives the
interrupts from CSE to write the variables. Then we would have a consistency
on the feature.
Does this seems ok for you?

-- 
Sylvain

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#1309457

On Fri, 08 Jan, at 02:57:13PM, Sylvain Chouleur wrote:
> 
> I understand, like I said above I'll modify efi_interruptible handlers to
> call legacy ones in case of panic context.
> I would like to avoid removing the panic part of this patch and take time
> to clean it before merging the whole.
 
OK, well at least split out the panic diddling into a separate patch
so that we can discuss the merits of it separately to the other, less
contentious changes.

> > Kconfig is a last resort because it's a build-time decision and
> > greatly limits the flexibility of the kernel. It becomes no longer
> > possible to run a single kernel image with various CONFIG_* enabled on
> > x86 hardware - you now need a special EFI_INTERRUPTIBLE build.
> >
> > Which apart from being a major headache for distributions in general
> > is generally frowned upon for the x86 architecture.
> >
> > If there's any way at all of making this a runtime decision that would
> > be much better.
> 
> I think the best would be to bind this driver with the one which receives the
> interrupts from CSE to write the variables. Then we would have a consistency
> on the feature.
> Does this seems ok for you?

I think that'd be an improvement, yeah.

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