Re: [PATCH V2 2/3] efi: Introduce efi_rts_workqueue and some infrastructure to invoke all efi_runtime_services()

[Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>]

On Tue, Mar 6, 2018 at 12:23 AM, Sai Praneeth Prakhya
<sai.praneeth.prakhya@intel.com> wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@intel.com>
>
> When a process requests the kernel to execute any efi_runtime_service(),
> the requested efi_runtime_service (represented as an identifier) and its
> arguments are packed into a struct named efi_runtime_work and queued
> onto work queue named efi_rts_wq. The caller then waits until the work
> is completed.
>
> Introduce some infrastructure:
> 1. Creating workqueue named efi_rts_wq
> 2. A macro (efi_queue_work()) that
>         a. populates efi_runtime_work
>         b. queues work onto efi_rts_wq and
>         c. waits until worker thread returns
>
> The caller thread has to wait until the worker thread returns, because
> it's dependent on the return status of efi_runtime_service() and, in
> specific cases, the arguments populated by efi_runtime_service(). Some
> efi_runtime_services() takes a pointer to buffer as an argument and
> fills up the buffer with requested data. For instance,
> efi_get_variable() and efi_get_next_variable(). Hence, caller process
> cannot just post the work and get going.
>
> Some facts about efi_runtime_services():
> 1. A quick look at all the efi_runtime_services() shows that any
> efi_runtime_service() has five or less arguments.
> 2. An argument of efi_runtime_service() can be a value (of any type)
> or a pointer (of any type).
> Hence, efi_runtime_work has five void pointers to store these arguments.
>
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Cc: Lee, Chun-Yi <jlee@suse.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Bhupesh Sharma <bhsharma@redhat.com>
> Cc: Ricardo Neri <ricardo.neri@intel.com>
> Cc: Ravi Shankar <ravi.v.shankar@intel.com>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: Peter Zijlstra <peter.zijlstra@intel.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/firmware/efi/efi.c              | 15 ++++++++
>  drivers/firmware/efi/runtime-wrappers.c | 61 +++++++++++++++++++++++++++++++++
>  include/linux/efi.h                     | 20 +++++++++++
>  3 files changed, 96 insertions(+)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 838b8efe639c..04b46c62f3ce 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -75,6 +75,8 @@ static unsigned long *efi_tables[] = {
>         &efi.mem_attr_table,
>  };
>
> +struct workqueue_struct *efi_rts_wq;
> +
>  static bool disable_runtime;
>  static int __init setup_noefi(char *arg)
>  {
> @@ -329,6 +331,19 @@ static int __init efisubsys_init(void)
>                 return 0;
>
>         /*
> +        * Since we process only one efi_runtime_service() at a time, an
> +        * ordered workqueue (which creates only one execution context)
> +        * should suffice all our needs.
> +        */
> +       efi_rts_wq = alloc_ordered_workqueue("efi_rts_workqueue", 0);

efi_rts_wq or efi_rts_workqueue?

> +       if (!efi_rts_wq) {
> +               pr_err("Failed to create efi_rts_workqueue, EFI runtime services "

Same here.

> +                      "disabled.\n");
> +               clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
> +               return 0;
> +       }
> +
> +       /*
>          * Clean DUMMY object calls EFI Runtime Service, set_variable(), so
>          * it should be invoked only after efi_rts_workqueue is ready.
>          */
> diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
> index ae54870b2788..649763171439 100644
> --- a/drivers/firmware/efi/runtime-wrappers.c
> +++ b/drivers/firmware/efi/runtime-wrappers.c
> @@ -1,6 +1,14 @@
>  /*
>   * runtime-wrappers.c - Runtime Services function call wrappers
>   *
> + * Implementation summary:
> + * -----------------------
> + * 1. When user/kernel thread requests to execute efi_runtime_service(),
> + * enqueue work to efi_rts_workqueue.
> + * 2. Caller thread waits until the work is finished because it's
> + * dependent on the return status and execution of efi_runtime_service().
> + * For instance, get_variable() and get_next_variable().
> + *
>   * Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org>
>   *
>   * Split off from arch/x86/platform/efi/efi.c
> @@ -22,6 +30,8 @@
>  #include <linux/mutex.h>
>  #include <linux/semaphore.h>
>  #include <linux/stringify.h>
> +#include <linux/workqueue.h>
> +
>  #include <asm/efi.h>
>
>  /*
> @@ -33,6 +43,57 @@
>  #define __efi_call_virt(f, args...) \
>         __efi_call_virt_pointer(efi.systab->runtime, f, args)
>
> +/* efi_runtime_service() function identifiers */
> +enum {
> +       GET_TIME,
> +       SET_TIME,
> +       GET_WAKEUP_TIME,
> +       SET_WAKEUP_TIME,
> +       GET_VARIABLE,
> +       GET_NEXT_VARIABLE,
> +       SET_VARIABLE,
> +       SET_VARIABLE_NONBLOCKING,
> +       QUERY_VARIABLE_INFO,
> +       QUERY_VARIABLE_INFO_NONBLOCKING,
> +       GET_NEXT_HIGH_MONO_COUNT,
> +       RESET_SYSTEM,
> +       UPDATE_CAPSULE,
> +       QUERY_CAPSULE_CAPS,
> +};

Much cleaner now :-)

> +
> +/*
> + * efi_queue_work:     Queue efi_runtime_service() and wait until it's done
> + * @rts:               efi_runtime_service() function identifier
> + * @rts_arg<1-5>:      efi_runtime_service() function arguments
> + *
> + * Accesses to efi_runtime_services() are serialized by a binary
> + * semaphore (efi_runtime_lock) and caller waits until the work is
> + * finished, hence _only_ one work is queued at a time and the queued
> + * work gets flushed.
> + */
> +#define efi_queue_work(_rts, _arg1, _arg2, _arg3, _arg4, _arg5)                \
> +({                                                                     \
> +       struct efi_runtime_work efi_rts_work;                           \
> +                                                                       \
> +       INIT_WORK_ONSTACK(&efi_rts_work.work, efi_call_rts);            \
> +       efi_rts_work.func = _rts;                                       \
> +       efi_rts_work.arg1 = _arg1;                                      \
> +       efi_rts_work.arg2 = _arg2;                                      \
> +       efi_rts_work.arg3 = _arg3;                                      \
> +       efi_rts_work.arg4 = _arg4;                                      \
> +       efi_rts_work.arg5 = _arg5;                                      \
> +       /*                                                              \
> +        * queue_work() returns 0 if work was already on queue,         \
> +        * _ideally_ this should never happen.                          \
> +        */                                                             \
> +       if (queue_work(efi_rts_wq, &efi_rts_work.work))                 \
> +               flush_work(&efi_rts_work.work);                         \
> +       else                                                            \
> +               BUG();                                                  \

Thanks for the change! One remark, I would just do:

> +       if (!queue_work(efi_rts_wq, &efi_rts_work.work))                \
> +               BUG();                                                  \

And then you can unindent:

> +       flush_work(&efi_rts_work.work);                         \

> +                                                                       \
> +       efi_rts_work.status;                                            \
> +})
> +
>  void efi_call_virt_check_flags(unsigned long flags, const char *call)
>  {
>         unsigned long cur_flags, mismatch;
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index c4efb3ef0dfa..bb06b71af55c 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -1652,4 +1652,24 @@ struct linux_efi_tpm_eventlog {
>
>  extern int efi_tpm_eventlog_init(void);
>
> +/*
> + * efi_runtime_work:   Details of EFI Runtime Service work
> + * @func:              EFI Runtime Service function identifier
> + * @arg<1-5>:          EFI Runtime Service function arguments
> + * @status:            Status of executing EFI Runtime Service
> + */
> +struct efi_runtime_work {
> +       u8 func;
> +       void *arg1;
> +       void *arg2;
> +       void *arg3;
> +       void *arg4;
> +       void *arg5;
> +       efi_status_t status;
> +       struct work_struct work;
> +};

Why is efi_runtime_work in the .h at all?

Please CC me for the next version! :-)

Cheers,
Miguel

> +
> +/* Workqueue to queue EFI Runtime Services */
> +extern struct workqueue_struct *efi_rts_wq;
> +
>  #endif /* _LINUX_EFI_H */
> --
> 2.7.4
>