[PATCH v4 1/2] cpufreq: acpi-cpufreq: fix P-state index mismatch in extract_io()

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

When policy->freq_table is built in acpi_cpufreq_cpu_init(), entries
that are not lower in frequency than the previous one are skipped.
For each remaining entry, freq_table[].driver_data stores the
original ACPI P-state index, so the index space of freq_table no
longer matches perf->states[].

extract_io() currently walks perf->states[] with index i and uses the
same i to index policy->freq_table[i]. When duplicate frequencies
exist, this can associate a P-state status with the frequency of a
different P-state. It can also access an invalid or sentinel entry in
freq_table when the number of entries in perf->states[] is greater than
the number of entries remaining in the frequency table.

extract_io() is used on ACPI_ADR_SPACE_SYSTEM_IO platforms by the
frequency verification path, which is enabled by the
acpi_pstate_strict module parameter. With the mismatched lookup,
check_freqs() can fail to match the frequency of the P-state that
drv_write() has already programmed. It then sleeps through all 100
iterations - at least ~1 ms of usleep_range() plus 100 cross-CPU
calls and I/O port reads, all with policy->rwsem held, and
.target_index() returns -EAGAIN, leaving perf->state at its previous
value while the hardware is running at the newly requested P-state.

The cpufreq core consequently keeps policy->cur at the old frequency.
Since __cpufreq_driver_target() returns early when the requested
frequency equals policy->cur, the driver is not called again for that
frequency and the control register is not rewritten. The hardware can
therefore remain at a frequency that differs from the frequency known
to the cpufreq core.

Fix this by iterating over policy->freq_table and using
pos->driver_data as the original ACPI P-state index when accessing
perf->states[], as extract_msr() already does.

Fixes: fe27cb358835 ("[CPUFREQ][2/8] acpi: reorganize code to make MSR support addition easier")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
---
 drivers/cpufreq/acpi-cpufreq.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 10ea603..a797bb2 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -197,14 +197,13 @@ static unsigned extract_io(struct cpufreq_policy *policy, u32 value)
 {
 	struct acpi_cpufreq_data *data = policy->driver_data;
 	struct acpi_processor_performance *perf;
-	int i;
+	struct cpufreq_frequency_table *pos;
 
 	perf = to_perf_data(data);
 
-	for (i = 0; i < perf->state_count; i++) {
-		if (value == perf->states[i].status)
-			return policy->freq_table[i].frequency;
-	}
+	cpufreq_for_each_entry(pos, policy->freq_table)
+		if (value == perf->states[pos->driver_data].status)
+			return pos->frequency;
 	return 0;
 }
 
-- 
2.9.4