diff mbox series

[v15,04/12] x86/smpboot: Reference count on smpboot_setup_warm_reset_vector()

Message ID 20230316222109.1940300-5-usama.arif@bytedance.com (mailing list archive)
State New, archived
Headers show
Series Parallel CPU bringup for x86_64 | expand

Commit Message

Usama Arif March 16, 2023, 10:21 p.m. UTC 
From: David Woodhouse <dwmw@amazon.co.uk>

When bringing up a secondary CPU from do_boot_cpu(), the warm reset flag
is set in CMOS and the starting IP for the trampoline written inside the
BDA at 0x467. Once the CPU is running, the CMOS flag is unset and the
value in the BDA cleared.

To allow for parallel bringup of CPUs, add a reference count to track the
number of CPUs currently bring brought up, and clear the state only when
the count reaches zero.

Since the RTC spinlock is required to write to the CMOS, it can be used
for mutual exclusion on the refcount too.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Kim Phillips <kim.phillips@amd.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
 arch/x86/kernel/smpboot.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

Comments

Borislav Petkov March 21, 2023, 11:41 a.m. UTC | #1 
On Thu, Mar 16, 2023 at 10:21:01PM +0000, Usama Arif wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> When bringing up a secondary CPU from do_boot_cpu(), the warm reset flag
> is set in CMOS and the starting IP for the trampoline written inside the
> BDA at 0x467. Once the CPU is running, the CMOS flag is unset and the
> value in the BDA cleared.
> 
> To allow for parallel bringup of CPUs, add a reference count to track the
> number of CPUs currently bring brought up, and clear the state only when

s/bring //

> the count reaches zero.
David Woodhouse March 21, 2023, 11:43 a.m. UTC | #2 
On 21 March 2023 11:41:15 GMT, Borislav Petkov <bp@alien8.de> wrote:
>On Thu, Mar 16, 2023 at 10:21:01PM +0000, Usama Arif wrote:
>> From: David Woodhouse <dwmw@amazon.co.uk>
>> 
>> When bringing up a secondary CPU from do_boot_cpu(), the warm reset flag
>> is set in CMOS and the starting IP for the trampoline written inside the
>> BDA at 0x467. Once the CPU is running, the CMOS flag is unset and the
>> value in the BDA cleared.
>> 
>> To allow for parallel bringup of CPUs, add a reference count to track the
>> number of CPUs currently bring brought up, and clear the state only when
>
>s/bring //

"being", I think.
diff mbox series

Patch

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 55cad72715d9..3a793772a2aa 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -121,17 +121,20 @@  int arch_update_cpu_topology(void)
 	return retval;
 }
 
+
+static unsigned int smpboot_warm_reset_vector_count;
+
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0xa, 0xf);
+	if (!smpboot_warm_reset_vector_count++) {
+		CMOS_WRITE(0xa, 0xf);
+		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) = start_eip >> 4;
+		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = start_eip & 0xf;
+	}
 	spin_unlock_irqrestore(&rtc_lock, flags);
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
-							start_eip >> 4;
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
-							start_eip & 0xf;
 }
 
 static inline void smpboot_restore_warm_reset_vector(void)
@@ -143,10 +146,12 @@  static inline void smpboot_restore_warm_reset_vector(void)
 	 * to default values.
 	 */
 	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0, 0xf);
+	if (!--smpboot_warm_reset_vector_count) {
+		CMOS_WRITE(0, 0xf);
+		*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
+	}
 	spin_unlock_irqrestore(&rtc_lock, flags);
 
-	*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
 }
 
 /*