Re: [patch 5/6] x86/smp: Split sending INIT IPI out into a helper function

From: Mika Penttilä
Date: Sun Jun 04 2023 - 00:05:24 EST


Hi,

On 3.6.2023 23.07, Thomas Gleixner wrote:
Putting CPUs into INIT is a safer place during kexec() to park CPUs.

Split the INIT assert/deassert sequence out so it can be reused.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/kernel/smpboot.c | 51 +++++++++++++++++++---------------------------
1 file changed, 22 insertions(+), 29 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -853,47 +853,40 @@ wakeup_secondary_cpu_via_nmi(int apicid,
return (send_status | accept_status);
}
-static int
-wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
+static void send_init_sequence(int phys_apicid)
{
- unsigned long send_status = 0, accept_status = 0;
- int maxlvt, num_starts, j;
-
- maxlvt = lapic_get_maxlvt();
+ int maxlvt = lapic_get_maxlvt();
- /*
- * Be paranoid about clearing APIC errors.
- */
+ /* Be paranoid about clearing APIC errors. */
if (APIC_INTEGRATED(boot_cpu_apic_version)) {
- if (maxlvt > 3) /* Due to the Pentium erratum 3AP. */
+ /* Due to the Pentium erratum 3AP. */
+ if (maxlvt > 3)
apic_write(APIC_ESR, 0);
apic_read(APIC_ESR);
}
- pr_debug("Asserting INIT\n");
-
- /*
- * Turn INIT on target chip
- */
- /*
- * Send IPI
- */
- apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT,
- phys_apicid);
-
- pr_debug("Waiting for send to finish...\n");
- send_status = safe_apic_wait_icr_idle();
+ /* Assert INIT on the target CPU */
+ apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT, phys_apicid);
+ safe_apic_wait_icr_idle();
udelay(init_udelay);
- pr_debug("Deasserting INIT\n");
-
- /* Target chip */
- /* Send IPI */
+ /* Deassert INIT on the target CPU */
apic_icr_write(APIC_INT_LEVELTRIG | APIC_DM_INIT, phys_apicid);
+ safe_apic_wait_icr_idle();
+}
+
+/*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ */
+static int wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
+{
+ unsigned long send_status = 0, accept_status = 0;
+ int maxlvt, num_starts, j;
+
+ preempt_disable();

This seems like an unbalanced preempt disable..

- pr_debug("Waiting for send to finish...\n");
- send_status = safe_apic_wait_icr_idle();
+ send_init_sequence(phys_apicid);
mb();



--Mika