Commit a7dd183f authored by Patryk Wlazlyn's avatar Patryk Wlazlyn Committed by Dave Hansen
Browse files

x86/smp: Allow calling mwait_play_dead with an arbitrary hint 



Introduce a helper function to allow offlined CPUs to enter idle states
with a specific MWAIT hint. The new helper will be used in subsequent
patches by the acpi_idle and intel_idle drivers.

No functional change intended.

Signed-off-by: default avatarPatryk Wlazlyn <patryk.wlazlyn@linux.intel.com>
Signed-off-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarGautham R. Shenoy <gautham.shenoy@amd.com>
Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/all/20250205155211.329780-2-artem.bityutskiy%40linux.intel.com
parent 1e66d6cf

arch/x86/include/asm/smp.h

+3 −0
Original line number Diff line number Diff line
@@ -114,6 +114,7 @@ void wbinvd_on_cpu(int cpu); 
int wbinvd_on_all_cpus(void);



void smp_kick_mwait_play_dead(void);

void mwait_play_dead(unsigned int eax_hint);



void native_smp_send_reschedule(int cpu);

void native_send_call_func_ipi(const struct cpumask *mask);
@@ -164,6 +165,8 @@ static inline struct cpumask *cpu_llc_shared_mask(int cpu) 
{

	return (struct cpumask *)cpumask_of(0);

}



static inline void mwait_play_dead(unsigned int eax_hint) { }

#endif /* CONFIG_SMP */



#ifdef CONFIG_DEBUG_NMI_SELFTEST

arch/x86/kernel/smpboot.c

+47 −41
Original line number Diff line number Diff line
@@ -1258,47 +1258,9 @@ void play_dead_common(void) 
	local_irq_disable();

}



/*

 * We need to flush the caches before going to sleep, lest we have

 * dirty data in our caches when we come back up.

 */

static inline void mwait_play_dead(void)

void __noreturn mwait_play_dead(unsigned int eax_hint)

{

	struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead);

	unsigned int eax, ebx, ecx, edx;

	unsigned int highest_cstate = 0;

	unsigned int highest_subcstate = 0;

	int i;



	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||

	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)

		return;

	if (!this_cpu_has(X86_FEATURE_MWAIT))

		return;

	if (!this_cpu_has(X86_FEATURE_CLFLUSH))

		return;



	eax = CPUID_LEAF_MWAIT;

	ecx = 0;

	native_cpuid(&eax, &ebx, &ecx, &edx);



	/*

	 * eax will be 0 if EDX enumeration is not valid.

	 * Initialized below to cstate, sub_cstate value when EDX is valid.

	 */

	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) {

		eax = 0;

	} else {

		edx >>= MWAIT_SUBSTATE_SIZE;

		for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {

			if (edx & MWAIT_SUBSTATE_MASK) {

				highest_cstate = i;

				highest_subcstate = edx & MWAIT_SUBSTATE_MASK;

			}

		}

		eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |

			(highest_subcstate - 1);

	}



	/* Set up state for the kexec() hack below */

	md->status = CPUDEAD_MWAIT_WAIT;
@@ -1319,7 +1281,7 @@ static inline void mwait_play_dead(void) 
		mb();

		__monitor(md, 0, 0);

		mb();

		__mwait(eax, 0);

		__mwait(eax_hint, 0);



		if (READ_ONCE(md->control) == CPUDEAD_MWAIT_KEXEC_HLT) {

			/*
@@ -1341,6 +1303,50 @@ static inline void mwait_play_dead(void) 
	}

}



/*

 * We need to flush the caches before going to sleep, lest we have

 * dirty data in our caches when we come back up.

 */

static inline void mwait_play_dead_cpuid_hint(void)

{

	unsigned int eax, ebx, ecx, edx;

	unsigned int highest_cstate = 0;

	unsigned int highest_subcstate = 0;

	int i;



	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||

	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)

		return;

	if (!this_cpu_has(X86_FEATURE_MWAIT))

		return;

	if (!this_cpu_has(X86_FEATURE_CLFLUSH))

		return;



	eax = CPUID_LEAF_MWAIT;

	ecx = 0;

	native_cpuid(&eax, &ebx, &ecx, &edx);



	/*

	 * eax will be 0 if EDX enumeration is not valid.

	 * Initialized below to cstate, sub_cstate value when EDX is valid.

	 */

	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) {

		eax = 0;

	} else {

		edx >>= MWAIT_SUBSTATE_SIZE;

		for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {

			if (edx & MWAIT_SUBSTATE_MASK) {

				highest_cstate = i;

				highest_subcstate = edx & MWAIT_SUBSTATE_MASK;

			}

		}

		eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |

			(highest_subcstate - 1);

	}



	mwait_play_dead(eax);

}



/*

 * Kick all "offline" CPUs out of mwait on kexec(). See comment in

 * mwait_play_dead().
@@ -1391,7 +1397,7 @@ void native_play_dead(void) 
	play_dead_common();

	tboot_shutdown(TB_SHUTDOWN_WFS);



	mwait_play_dead();

	mwait_play_dead_cpuid_hint();

	if (cpuidle_play_dead())

		hlt_play_dead();

}