Re: [PATCH] i386/apic: Add hint on boot failure because of disabling x2APIC

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 6/6/24 16:08, Zhao Liu wrote:
> Currently, the Q35 supports up to 4096 vCPUs (since v9.0), but for TCG
> cases, if x2APIC is not actively enabled to boot more than 255 vCPUs (
> e.g., qemu-system-i386 -M pc-q35-9.0 -smp 666), the following error is
> reported:
> 
> Unexpected error in apic_common_set_id() at ../hw/intc/apic_common.c:449:
> qemu-system-i386: APIC ID 255 requires x2APIC feature in CPU
> Aborted (core dumped)
> 
> This error can be resolved by setting x2apic=on in -cpu. In order to
> better help users deal with this scenario, add the error hint to
> instruct users on how to enable the x2apic feature.

Why not automatically set x2apic=on in this case instead?

> Then, the error
> report becomes the following:
> 
> Unexpected error in apic_common_set_id() at ../hw/intc/apic_common.c:448:
> qemu-system-i386: APIC ID 255 requires x2APIC feature in CPU
> Try x2apic=on in -cpu.
> Aborted (core dumped)
> 
> Note since @errp is &error_abort, error_append_hint() can't be applied
> on @errp. And in order to separate the exact error message from the
> (perhaps effectively) hint, adding a hint via error_append_hint() is
> also necessary. Therefore, introduce @local_error in
> apic_common_set_id() to handle both the error message and the error
> hint.
> 
> Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>   hw/intc/apic_common.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>