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Subject[PATCH V3 2/3] efi: Introduce efi_queue_work() to queue any efi_runtime_service() on efi_rts_wq
Date
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 efi_queue_work() that 1. Populates efi_runtime_work 2. Queues
work onto efi_rts_wq and 3. Waits until worker thread returns.

The caller thread has to wait until the worker thread returns, because
it depends 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: Naresh Bhat <naresh.bhat@linaro.org>
Cc: Ricardo Neri <ricardo.neri@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
---
drivers/firmware/efi/runtime-wrappers.c | 80 +++++++++++++++++++++++++++++++++
1 file changed, 80 insertions(+)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index ae54870b2788..a9866045ed52 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_wq.
+ * 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 +43,76 @@
#define __efi_call_virt(f, args...) \
__efi_call_virt_pointer(efi.systab->runtime, f, args)

+/* efi_runtime_service() function identifiers */
+enum efi_rts_ids {
+ 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,
+};
+
+/*
+ * 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 {
+ void *arg1;
+ void *arg2;
+ void *arg3;
+ void *arg4;
+ void *arg5;
+ efi_status_t status;
+ struct work_struct work;
+ enum efi_rts_ids efi_rts_id;
+};
+
+/*
+ * 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; \
+ efi_rts_work.status = EFI_ABORTED; \
+ \
+ INIT_WORK_ONSTACK(&efi_rts_work.work, efi_call_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; \
+ efi_rts_work.efi_rts_id = _rts; \
+ \
+ /* \
+ * 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 \
+ pr_err("Failed to queue work to efi_rts_wq.\n"); \
+ \
+ efi_rts_work.status; \
+})
+
void efi_call_virt_check_flags(unsigned long flags, const char *call)
{
unsigned long cur_flags, mismatch;
--
2.7.4
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