x86/cpu: identify uninitialized CPU data using BAD_APICID

[PATCH] x86/cpu: identify uninitialized CPU data using BAD_APICID

Posted by Roger Pau Monne 3 days, 1 hour ago

Uninitialized cpu_data[] entries have the apicid field set to BAD_APICID,
not boot_cpu_data.apicid.  Fix the check in cpu_smpboot_free() to use the
correct condition.

Fixes: 7126b7f806d5 ("x86/CPU: re-work populating of cpu_data[]")
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/arch/x86/smpboot.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 491cbbba33ae..ff05955bae40 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -961,8 +961,7 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
      * In that case the socket number cannot be relied upon, but the respective
      * socket_cpumask[] slot also wouldn't have been set.
      */
-    if ( c[cpu].apicid != boot_cpu_data.apicid &&
-         cpumask_empty(socket_cpumask[socket]) )
+    if ( c[cpu].apicid != BAD_APICID && cpumask_empty(socket_cpumask[socket]) )
     {
         xfree(socket_cpumask[socket]);
         socket_cpumask[socket] = NULL;
-- 
2.53.0

Re: [PATCH] x86/cpu: identify uninitialized CPU data using BAD_APICID

Posted by Andrew Cooper 2 days, 22 hours ago

On 30/04/2026 12:46 pm, Roger Pau Monne wrote:
> Uninitialized cpu_data[] entries have the apicid field set to BAD_APICID,
> not boot_cpu_data.apicid.  Fix the check in cpu_smpboot_free() to use the
> correct condition.
>
> Fixes: 7126b7f806d5 ("x86/CPU: re-work populating of cpu_data[]")
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>  xen/arch/x86/smpboot.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
> index 491cbbba33ae..ff05955bae40 100644
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -961,8 +961,7 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
>       * In that case the socket number cannot be relied upon, but the respective
>       * socket_cpumask[] slot also wouldn't have been set.
>       */
> -    if ( c[cpu].apicid != boot_cpu_data.apicid &&
> -         cpumask_empty(socket_cpumask[socket]) )
> +    if ( c[cpu].apicid != BAD_APICID && cpumask_empty(socket_cpumask[socket]) )
>      {
>          xfree(socket_cpumask[socket]);
>          socket_cpumask[socket] = NULL;

Yet more fallout from that change...

This is the singular use of apicid.  We should consider removing it, but
that's a change for later.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Re: [PATCH] x86/cpu: identify uninitialized CPU data using BAD_APICID

Posted by Teddy Astie 3 days ago

Le 30/04/2026 à 13:47, Roger Pau Monne a écrit :
> Uninitialized cpu_data[] entries have the apicid field set to BAD_APICID,
> not boot_cpu_data.apicid.  Fix the check in cpu_smpboot_free() to use the
> correct condition.
> 
> Fixes: 7126b7f806d5 ("x86/CPU: re-work populating of cpu_data[]")
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>   xen/arch/x86/smpboot.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
> index 491cbbba33ae..ff05955bae40 100644
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -961,8 +961,7 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
>        * In that case the socket number cannot be relied upon, but the respective
>        * socket_cpumask[] slot also wouldn't have been set.
>        */
> -    if ( c[cpu].apicid != boot_cpu_data.apicid &&
> -         cpumask_empty(socket_cpumask[socket]) )
> +    if ( c[cpu].apicid != BAD_APICID && cpumask_empty(socket_cpumask[socket]) )
>       {
>           xfree(socket_cpumask[socket]);
>           socket_cpumask[socket] = NULL;

Reviewed-by: Teddy Astie <teddy.astie@vates.tech>


-- 
Teddy Astie | Vates XCP-ng Developer

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