Re: [PATCH v3 2/2] ppc/spapr: Initialize max_cpus limit to SPAPR_IRQ_NR_IPIS.

[Kowshik Jois B S]

On 23/11/23 14:21, Cédric Le Goater wrote:

> On
>       11/23/23 06:57, Harsh Prateek Bora wrote:
>       
> > Initialize the machine specific max_cpus
> >         limit as per the maximum range
> >         
> >         of CPU IPIs available. Keeping between 4096 to 8192 will throw
> >         IRQ not
> >         
> >         free error due to XIVE/XICS limitation and keeping beyond 8192
> >         will hit
> >         
> >         assert in tcg_region_init or spapr_xive_claim_irq.
> >         
> >         
> >         Logs:
> >         
> >         
> >         Without patch fix:
> >         
> >         
> >         [root@host build]# qemu-system-ppc64 -accel tcg -smp
> >         10,maxcpus=4097
> >         
> >         qemu-system-ppc64: IRQ 4096 is not free
> >         
> >         [root@host build]#
> >         
> >         
> >         On LPAR:
> >         
> >         [root@host build]# qemu-system-ppc64 -accel tcg -smp
> >         10,maxcpus=8193
> >         
> >         **
> >         
> >         ERROR:../tcg/region.c:774:tcg_region_init: assertion failed:
> >         
> >         (region_size >= 2 * page_size)
> >         
> >         Bail out! ERROR:../tcg/region.c:774:tcg_region_init: assertion
> >         failed:
> >         
> >         (region_size >= 2 * page_size)
> >         
> >         Aborted (core dumped)
> >         
> >         [root@host build]#
> >         
> >         
> >         On x86:
> >         
> >         [root@host build]# qemu-system-ppc64 -accel tcg -smp
> >         10,maxcpus=8193
> >         
> >         qemu-system-ppc64: ../hw/intc/spapr_xive.c:596:
> >         spapr_xive_claim_irq:
> >         
> >         Assertion `lisn < xive->nr_irqs' failed.
> >         
> >         Aborted (core dumped)
> >         
> >         [root@host build]#
> >         
> >         
> >         With patch fix:
> >         
> >         [root@host build]# qemu-system-ppc64 -accel tcg -smp
> >         10,maxcpus=4097
> >         
> >         qemu-system-ppc64: Invalid SMP CPUs 4097. The max CPUs supported
> >         by
> >         
> >         machine 'pseries-8.2' is 4096
> >         
> >         [root@host build]#
> >         
> >         
> >         Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> >         
> >       
>       
>       
>       Reviewed-by: Cédric Le Goater <clg@kaod.org>
>       
>       
>       Thanks,
>       
>       
>       C.
>       
>       
>       
>       
> > ---
> >         
> >           hw/ppc/spapr.c | 9 +++------
> >         
> >           1 file changed, 3 insertions(+), 6 deletions(-)
> >         
> >         
> >         diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> >         
> >         index df09aa9d6a..222d926f46 100644
> >         
> >         --- a/hw/ppc/spapr.c
> >         
> >         +++ b/hw/ppc/spapr.c
> >         
> >         @@ -4647,13 +4647,10 @@ static void
> >         spapr_machine_class_init(ObjectClass *oc, void *data)
> >         
> >               mc->block_default_type = IF_SCSI;
> >         
> >                 /*
> >         
> >         -     * Setting max_cpus to INT32_MAX. Both KVM and TCG max_cpus
> >         values
> >         
> >         -     * should be limited by the host capability instead of
> >         hardcoded.
> >         
> >         -     * max_cpus for KVM guests will be checked in kvm_init(),
> >         and TCG
> >         
> >         -     * guests are welcome to have as many CPUs as the host are
> >         capable
> >         
> >         -     * of emulate.
> >         
> >         +     * While KVM determines max cpus in kvm_init() using
> >         kvm_max_vcpus(),
> >         
> >         +     * In TCG the limit is restricted by the range of CPU IPIs
> >         available.
> >         
> >                */
> >         
> >         -    mc->max_cpus = INT32_MAX;
> >         
> >         +    mc->max_cpus = SPAPR_IRQ_NR_IPIS;
> >         
> >                 mc->no_parallel = 1;
> >         
> >               mc->default_boot_order = "";
> >         
> >       
>       
> I've applied these patches and verified on the latest upstream qemu. The code is working as expected.
>
> Tested-by: Kowshik Jois<kowsjois@linux.ibm.com>
>

>