With the tokens for all implemented RTAS functions now available via
rtas_function_token(), which is optimal and safe for arbitrary
contexts, there is no need to use rtas_token() or cache its result.

Most conversions are trivial, but a few are worth describing in more
detail:

* Error injection token comparisons for lockdown purposes are
  consolidated into a simple predicate: token_is_restricted_errinjct().

* A couple of special cases in block_rtas_call() do not use
  rtas_token() but perform string comparisons against names in the
  function table. These are converted to compare against token values
  instead, which is logically equivalent but less expensive.

* The lookup for the ibm,os-term token can be deferred until needed,
  instead of caching it at boot to avoid device tree traversal during
  panic.

* Since rtas_function_token() accesses a read-only data structure
  without taking any locks, xmon's lookup of set-indicator can be
  performed as needed instead of cached at startup.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-20-26929c8cce78@linux.ibm.com

Users of rtas_token() supply a string argument that can't be validated
at build time. A typo or misspelling has to be caught by inspection or
by observing wrong behavior at runtime.

Since the core RTAS code now has consolidated the names of all
possible RTAS functions and mapped them to their tokens, token lookup
can be implemented using symbolic constants to index a static array.

So introduce rtas_function_token(), a replacement API which does that,
along with a rtas_service_present()-equivalent helper,
rtas_function_implemented(). Callers supply an opaque predefined
function handle which is used internally to index the function
table. Typos or other inappropriate arguments yield build errors, and
the function handle is a type that can't be easily confused with RTAS
tokens or other integer types.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-19-26929c8cce78@linux.ibm.com

Various pseries-specific RTAS functions take a temporary "work area"
parameter - a buffer in memory accessible to RTAS. Typically such
functions are passed the statically allocated rtas_data_buf buffer as
the argument. This buffer is protected by a global spinlock. So users
of rtas_data_buf cannot perform sleeping operations while accessing
the buffer.

Most RTAS functions that have a work area parameter can return a
status (-2/990x) that indicates that the caller should retry. Before
retrying, the caller may need to reschedule or sleep (see
rtas_busy_delay() for details). This combination of factors
leads to uncomfortable constructions like this:

	do {
		spin_lock(&rtas_data_buf_lock);
		rc = rtas_call(token, __pa(rtas_data_buf, ...);
		if (rc == 0) {
			/* parse or copy out rtas_data_buf contents */
		}
		spin_unlock(&rtas_data_buf_lock);
	} while (rtas_busy_delay(rc));

Another unfortunately common way of handling this is for callers to
blithely ignore the possibility of a -2/990x status and hope for the
best.

If users were allowed to perform blocking operations while owning a
work area, the programming model would become less tedious and
error-prone. Users could schedule away, sleep, or perform other
blocking operations without having to release and re-acquire
resources.

We could continue to use a single work area buffer, and convert
rtas_data_buf_lock to a mutex. But that would impose an unnecessarily
coarse serialization on all users. As awkward as the current design
is, it prevents longer running operations that need to repeatedly use
rtas_data_buf from blocking the progress of others.

There are more considerations. One is that while 4KB is fine for all
current in-kernel uses, some RTAS calls can take much smaller buffers,
and some (VPD, platform dumps) would likely benefit from larger
ones. Another is that at least one RTAS function (ibm,get-vpd)
has *two* work area parameters. And finally, we should expect the
number of work area users in the kernel to increase over time as we
introduce lockdown-compatible ABIs to replace less safe use cases
based on sys_rtas/librtas.

So a special-purpose allocator for RTAS work area buffers seems worth
trying.

Properties:

* The backing memory for the allocator is reserved early in boot in
  order to satisfy RTAS addressing requirements, and then managed with
  genalloc.
* Allocations can block, but they never fail (mempool-like).
* Prioritizes first-come, first-serve fairness over throughput.
* Early boot allocations before the allocator has been initialized are
  served via an internal static buffer.

Intended to replace rtas_data_buf. New code that needs RTAS work area
buffers should prefer this API.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-12-26929c8cce78@linux.ibm.com

Decompose the RTAS entry C code into tracing and non-tracing variants,
calling the just-added tracepoints in the tracing-enabled path. Skip
tracing in contexts known to be unsafe (real mode, CPU offline).

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-11-26929c8cce78@linux.ibm.com

Make do_enter_rtas() take a pointer to struct rtas_args and do the
__pa() conversion in one place instead of leaving it to callers. This
also makes it possible to introduce enter/exit tracepoints that access
the rtas_args struct fields.

There's no apparent reason to force inlining of do_enter_rtas()
either, and it seems to bloat the code a bit. Let the compiler decide.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-9-26929c8cce78@linux.ibm.com

The core RTAS support code and its clients perform two types of lookup
for RTAS firmware function information.

First, mapping a known function name to a token. The typical use case
invokes rtas_token() to retrieve the token value to pass to
rtas_call(). rtas_token() relies on of_get_property(), which performs
a linear search of the /rtas node's property list under a lock with
IRQs disabled.

Second, and less common: given a token value, looking up some
information about the function. The primary example is the sys_rtas
filter path, which linearly scans a small table to match the token to
a rtas_filter struct. Another use case to come is RTAS entry/exit
tracepoints, which will require efficient lookup of function names
from token values. Currently there is no general API for this.

We need something much like the existing rtas_filters table, but more
general and organized to facilitate efficient lookups.

Introduce:

* A new rtas_function type, aggregating function name, token,
  and filter. Other function characteristics could be added in the
  future.

* An array of rtas_function, where each element corresponds to a known
  RTAS function. All information in the table is static save the token
  values, which are derived from the device tree at boot. The array is
  sorted by function name to allow binary search.

* A named constant for each known RTAS function, used to index the
  function array. These also will be used in a client-facing API to be
  added later.

* An xarray that maps valid tokens to rtas_function objects.

Fold the existing rtas_filter table into the new rtas_function array,
with the appropriate adjustments to block_rtas_call(). Remove
now-redundant fields from struct rtas_filter. Preserve the function of
the CONFIG_CPU_BIG_ENDIAN guard in the current filter table by
introducing a per-function flag that is set for the function entries
related to pseries LPAR migration. These have never had working users
via sys_rtas on ppc64le; see commit de0f7349a0dd ("powerpc/rtas:
prevent suspend-related sys_rtas use on LE").

Convert rtas_token() to use a lockless binary search on the function
table. Fall back to the old behavior for lookups against names that
are not known to be RTAS functions, but issue a warning. rtas_token()
is for function names; it is not a general facility for accessing
arbitrary properties of the /rtas node. All known misuses of
rtas_token() have been converted to more appropriate of_ APIs in
preceding changes.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-8-26929c8cce78@linux.ibm.com

Some RTAS functions that have work area parameters impose alignment
requirements on the work area passed to them by the OS. Examples
include:

- ibm,configure-connector
- ibm,update-nodes
- ibm,update-properties

4KB is the greatest alignment required by PAPR for such
buffers. rtas_data_buf used to have a __page_aligned attribute in the
arch/ppc64 days, but that was changed to __cacheline_aligned for
unknown reasons by commit 033ef338b6e0 ("powerpc: Merge rtas.c into
arch/powerpc/kernel"). That works out to 128-byte alignment
on ppc64, which isn't right.

This was found by inspection and I'm not aware of any real problems
caused by this. Either current RTAS implementations don't enforce the
alignment constraints, or rtas_data_buf is always being placed at a
4KB boundary by accident (or both, perhaps).

Use __aligned(SZ_4K) to ensure the rtas_data_buf has alignment
appropriate for all users.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Fixes: 033ef338b6e0 ("powerpc: Merge rtas.c into arch/powerpc/kernel")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-6-26929c8cce78@linux.ibm.com

Some code that runs early in boot calls RTAS functions that can return
-2 or 990x statuses, which mean the caller should retry. An example is
pSeries_cmo_feature_init(), which invokes ibm,get-system-parameter but
treats these benign statuses as errors instead of retrying.

pSeries_cmo_feature_init() and similar code should be made to retry
until they succeed or receive a real error, using the usual pattern:

	do {
		rc = rtas_call(token, etc...);
	} while (rtas_busy_delay(rc));

But rtas_busy_delay() will perform a timed sleep on any 990x
status. This isn't safe so early in boot, before the CPU scheduler and
timer subsystem have initialized.

The -2 RTAS status is much more likely to occur during single-threaded
boot than 990x in practice, at least on PowerVM. This is because -2
usually means that RTAS made progress but exhausted its self-imposed
timeslice, while 990x is associated with concurrent requests from the
OS causing internal contention. Regardless, according to the language
in PAPR, the OS should be prepared to handle either type of status at
any time.

Add a fallback path to rtas_busy_delay() to handle this as safely as
possible, performing a small delay on 990x. Include a counter to
detect retry loops that aren't making progress and bail out. Add __ref
to rtas_busy_delay() since it now conditionally calls an __init
function.

This was found by inspection and I'm not aware of any real
failures. However, the implementation of rtas_busy_delay() before
commit 38f7b7067dae ("powerpc/rtas: rtas_busy_delay() improvements")
was not susceptible to this problem, so let's treat this as a
regression.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Fixes: 38f7b7067dae ("powerpc/rtas: rtas_busy_delay() improvements")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-1-26929c8cce78@linux.ibm.com

At the time commit f97bb36f705d ("powerpc/rtas: Turn rtas lock into a
raw spinlock") was written, the spinlock lockup detection code called
__delay(), which will not make progress if the timebase is not
advancing. Since the interprocessor timebase synchronization sequence
for chrp, cell, and some now-unsupported Power models can temporarily
freeze the timebase through an RTAS function (freeze-time-base), the
lock that serializes most RTAS calls was converted to arch_spinlock_t
to prevent kernel hangs in the lockup detection code.

However, commit bc88c10d7e69 ("locking/spinlock/debug: Remove spinlock
lockup detection code") removed that inconvenient property from the
lock debug code several years ago. So now it should be safe to
reintroduce generic locks into the RTAS support code, primarily to
increase lockdep coverage.

Making rtas_lock a spinlock_t would violate lock type nesting rules
because it can be acquired while holding raw locks, e.g. pci_lock and
irq_desc->lock. So convert it to raw_spinlock_t. There's no apparent
reason not to upgrade timebase_lock as well.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230124140448.45938-5-nathanl@linux.ibm.com

Only code internal to the RTAS subsystem needs access to the central
lock and parameter block. Remove these from the globally visible
'rtas' struct and make them file-static in rtas.c.

Some changed lines in rtas_call() lack appropriate spacing around
operators and cause checkpatch errors; fix these as well.

Suggested-by: Laurent Dufour <ldufour@linux.ibm.com>
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Laurent Dufour <laurent.dufour@fr.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230124140448.45938-4-nathanl@linux.ibm.com