Commit eac030b2 authored by Russell Currey's avatar Russell Currey Committed by Michael Ellerman
Browse files

powerpc/pseries: Rework lppaca_shared_proc() to avoid DEBUG_PREEMPT 



lppaca_shared_proc() takes a pointer to the lppaca which is typically
accessed through get_lppaca().  With DEBUG_PREEMPT enabled, this leads
to checking if preemption is enabled, for example:

  BUG: using smp_processor_id() in preemptible [00000000] code: grep/10693
  caller is lparcfg_data+0x408/0x19a0
  CPU: 4 PID: 10693 Comm: grep Not tainted 6.5.0-rc3 #2
  Call Trace:
    dump_stack_lvl+0x154/0x200 (unreliable)
    check_preemption_disabled+0x214/0x220
    lparcfg_data+0x408/0x19a0
    ...

This isn't actually a problem however, as it does not matter which
lppaca is accessed, the shared proc state will be the same.
vcpudispatch_stats_procfs_init() already works around this by disabling
preemption, but the lparcfg code does not, erroring any time
/proc/powerpc/lparcfg is accessed with DEBUG_PREEMPT enabled.

Instead of disabling preemption on the caller side, rework
lppaca_shared_proc() to not take a pointer and instead directly access
the lppaca, bypassing any potential preemption checks.

Fixes: f13c13a0 ("powerpc: Stop using non-architected shared_proc field in lppaca")
Signed-off-by: default avatarRussell Currey <ruscur@russell.cc>
[mpe: Rework to avoid needing a definition in paca.h and lppaca.h]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230823055317.751786-4-mpe@ellerman.id.au
parent 1aa00066

arch/powerpc/include/asm/lppaca.h

+9 −2
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <asm/types.h>

#include <asm/mmu.h>

#include <asm/firmware.h>

#include <asm/paca.h>



/*

 * The lppaca is the "virtual processor area" registered with the hypervisor,
@@ -105,14 +106,20 @@ struct lppaca { 
 */

#define LPPACA_OLD_SHARED_PROC		2



static inline bool lppaca_shared_proc(struct lppaca *l)

#ifdef CONFIG_PPC_PSERIES

/*

 * All CPUs should have the same shared proc value, so directly access the PACA

 * to avoid false positives from DEBUG_PREEMPT.

 */

static inline bool lppaca_shared_proc(void)

{

	struct lppaca *l = local_paca->lppaca_ptr;



	if (!firmware_has_feature(FW_FEATURE_SPLPAR))

		return false;

	return !!(l->__old_status & LPPACA_OLD_SHARED_PROC);

}



#ifdef CONFIG_PPC_PSERIES

#define get_lppaca()	(get_paca()->lppaca_ptr)

#endif

arch/powerpc/platforms/pseries/lpar.c

+1 −9
Original line number Diff line number Diff line
@@ -640,16 +640,8 @@ static const struct proc_ops vcpudispatch_stats_freq_proc_ops = { 


static int __init vcpudispatch_stats_procfs_init(void)

{

	/*

	 * Avoid smp_processor_id while preemptible. All CPUs should have

	 * the same value for lppaca_shared_proc.

	 */

	preempt_disable();

	if (!lppaca_shared_proc(get_lppaca())) {

		preempt_enable();

	if (!lppaca_shared_proc())

		return 0;

	}

	preempt_enable();



	if (!proc_create("powerpc/vcpudispatch_stats", 0600, NULL,

					&vcpudispatch_stats_proc_ops))

arch/powerpc/platforms/pseries/lparcfg.c

+2 −2
Original line number Diff line number Diff line
@@ -206,7 +206,7 @@ static void parse_ppp_data(struct seq_file *m) 
	           ppp_data.active_system_procs);



	/* pool related entries are appropriate for shared configs */

	if (lppaca_shared_proc(get_lppaca())) {

	if (lppaca_shared_proc()) {

		unsigned long pool_idle_time, pool_procs;



		seq_printf(m, "pool=%d\n", ppp_data.pool_num);
@@ -560,7 +560,7 @@ static int pseries_lparcfg_data(struct seq_file *m, void *v) 
		   partition_potential_processors);



	seq_printf(m, "shared_processor_mode=%d\n",

		   lppaca_shared_proc(get_lppaca()));

		   lppaca_shared_proc());



#ifdef CONFIG_PPC_64S_HASH_MMU

	if (!radix_enabled())

arch/powerpc/platforms/pseries/setup.c

+1 −1
Original line number Diff line number Diff line
@@ -849,7 +849,7 @@ static void __init pSeries_setup_arch(void) 
	if (firmware_has_feature(FW_FEATURE_LPAR)) {

		vpa_init(boot_cpuid);



		if (lppaca_shared_proc(get_lppaca())) {

		if (lppaca_shared_proc()) {

			static_branch_enable(&shared_processor);

			pv_spinlocks_init();

#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING

drivers/cpuidle/cpuidle-pseries.c

+1 −7
Original line number Diff line number Diff line
@@ -414,13 +414,7 @@ static int __init pseries_idle_probe(void) 
		return -ENODEV;



	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {

		/*

		 * Use local_paca instead of get_lppaca() since

		 * preemption is not disabled, and it is not required in

		 * fact, since lppaca_ptr does not need to be the value

		 * associated to the current CPU, it can be from any CPU.

		 */

		if (lppaca_shared_proc(local_paca->lppaca_ptr)) {

		if (lppaca_shared_proc()) {

			cpuidle_state_table = shared_states;

			max_idle_state = ARRAY_SIZE(shared_states);

		} else {