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Re: [PATCH v4 5/8] smp: Move cpu_up/down helpers to common code
- To: Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 13 Nov 2025 11:37:17 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 13 Nov 2025 10:37:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.11.2025 11:51, Mykyta Poturai wrote:
> This will reduce code duplication for the upcoming cpu hotplug support
> on Arm64 patch.
>
> SMT-disable enforcement check is moved into a separate
> architecture-specific function.
>
> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
Solely from an x86 perspective this looks okay to me, but on Arm you introduce
...
> --- a/xen/common/smp.c
> +++ b/xen/common/smp.c
> @@ -16,6 +16,7 @@
> * GNU General Public License for more details.
> */
>
> +#include <xen/cpu.h>
> #include <asm/hardirq.h>
> #include <asm/processor.h>
> #include <xen/spinlock.h>
> @@ -104,6 +105,37 @@ void smp_call_function_interrupt(void)
> irq_exit();
> }
>
> +long cf_check cpu_up_helper(void *data)
> +{
> + unsigned int cpu = (unsigned long)data;
> + int ret = cpu_up(cpu);
> +
> + /* Have one more go on EBUSY. */
> + if ( ret == -EBUSY )
> + ret = cpu_up(cpu);
> +
> + if ( !ret && arch_smt_cpu_disable(cpu) )
> + {
> + ret = cpu_down_helper(data);
> + if ( ret )
> + printk("Could not re-offline CPU%u (%d)\n", cpu, ret);
> + else
> + ret = -EPERM;
> + }
> +
> + return ret;
> +}
> +
> +long cf_check cpu_down_helper(void *data)
> +{
> + int cpu = (unsigned long)data;
> + int ret = cpu_down(cpu);
> + /* Have one more go on EBUSY. */
> + if ( ret == -EBUSY )
> + ret = cpu_down(cpu);
> + return ret;
> +}
...unreachable code, which - for the case when RUNTIME_CPU_CONTROL=n - won't
even be rectified by the next patch.
Jan
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