Commit 5d0fb1508e2d "spapr: consolidate the VCPU id numbering logic
in a single place" introduced a helper to detect thread0 of a virtual
core based on its VCPU id. This is used to create CPU core nodes in
the DT, but it is broken in TCG.

$ qemu-system-ppc64 -nographic -accel tcg -machine dumpdtb=dtb.bin \
                    -smp cores=16,maxcpus=16,threads=1
$ dtc -f -O dts dtb.bin | grep POWER8
                PowerPC,POWER8@0 {
                PowerPC,POWER8@8 {

instead of the expected 16 cores that we get with KVM:

$ dtc -f -O dts dtb.bin | grep POWER8
                PowerPC,POWER8@0 {
                PowerPC,POWER8@8 {
                PowerPC,POWER8@10 {
                PowerPC,POWER8@18 {
                PowerPC,POWER8@20 {
                PowerPC,POWER8@28 {
                PowerPC,POWER8@30 {
                PowerPC,POWER8@38 {
                PowerPC,POWER8@40 {
                PowerPC,POWER8@48 {
                PowerPC,POWER8@50 {
                PowerPC,POWER8@58 {
                PowerPC,POWER8@60 {
                PowerPC,POWER8@68 {
                PowerPC,POWER8@70 {
                PowerPC,POWER8@78 {

This happens because spapr_get_vcpu_id() maps VCPU ids to
cs->cpu_index in TCG mode. This confuses the code in
spapr_is_thread0_in_vcore(), since it assumes thread0 VCPU
ids to have a spapr->vsmt spacing.

    spapr_get_vcpu_id(cpu) % spapr->vsmt == 0

Actually, there's no real reason to expose cs->cpu_index instead
of the VCPU id, since we also generate it with TCG. Also we already
set it explicitly in spapr_set_vcpu_id(), so there's no real reason
either to call kvm_arch_vcpu_id() with KVM.

This patch unifies spapr_get_vcpu_id() to always return the computed
VCPU id both in TCG and KVM. This is one step forward towards KVM<->TCG
migration.

Fixes: 5d0fb1508e2d
Reported-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/ppc/spapr.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 83c9d66dd56f..d6fd0e666e74 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -3810,13 +3810,7 @@ static void spapr_pic_print_info(InterruptStatsProvider *obj,
 
 int spapr_get_vcpu_id(PowerPCCPU *cpu)
 {
-    CPUState *cs = CPU(cpu);
-
-    if (kvm_enabled()) {
-        return kvm_arch_vcpu_id(cs);
-    } else {
-        return cs->cpu_index;
-    }
+    return cpu->vcpu_id;
 }
 
 void spapr_set_vcpu_id(PowerPCCPU *cpu, int cpu_index, Error **errp)

On Fri, Feb 16, 2018 at 07:58:06PM +0100, Greg Kurz wrote:
> Commit 5d0fb1508e2d "spapr: consolidate the VCPU id numbering logic
> in a single place" introduced a helper to detect thread0 of a virtual
> core based on its VCPU id. This is used to create CPU core nodes in
> the DT, but it is broken in TCG.
> 
> $ qemu-system-ppc64 -nographic -accel tcg -machine dumpdtb=dtb.bin \
>                     -smp cores=16,maxcpus=16,threads=1
> $ dtc -f -O dts dtb.bin | grep POWER8
>                 PowerPC,POWER8@0 {
>                 PowerPC,POWER8@8 {
> 
> instead of the expected 16 cores that we get with KVM:
> 
> $ dtc -f -O dts dtb.bin | grep POWER8
>                 PowerPC,POWER8@0 {
>                 PowerPC,POWER8@8 {
>                 PowerPC,POWER8@10 {
>                 PowerPC,POWER8@18 {
>                 PowerPC,POWER8@20 {
>                 PowerPC,POWER8@28 {
>                 PowerPC,POWER8@30 {
>                 PowerPC,POWER8@38 {
>                 PowerPC,POWER8@40 {
>                 PowerPC,POWER8@48 {
>                 PowerPC,POWER8@50 {
>                 PowerPC,POWER8@58 {
>                 PowerPC,POWER8@60 {
>                 PowerPC,POWER8@68 {
>                 PowerPC,POWER8@70 {
>                 PowerPC,POWER8@78 {
> 
> This happens because spapr_get_vcpu_id() maps VCPU ids to
> cs->cpu_index in TCG mode. This confuses the code in
> spapr_is_thread0_in_vcore(), since it assumes thread0 VCPU
> ids to have a spapr->vsmt spacing.
> 
>     spapr_get_vcpu_id(cpu) % spapr->vsmt == 0
> 
> Actually, there's no real reason to expose cs->cpu_index instead
> of the VCPU id, since we also generate it with TCG. Also we already
> set it explicitly in spapr_set_vcpu_id(), so there's no real reason
> either to call kvm_arch_vcpu_id() with KVM.
> 
> This patch unifies spapr_get_vcpu_id() to always return the computed
> VCPU id both in TCG and KVM. This is one step forward towards KVM<->TCG
> migration.
> 
> Fixes: 5d0fb1508e2d
> Reported-by: Cédric Le Goater <clg@kaod.org>
> Signed-off-by: Greg Kurz <groug@kaod.org>

Applied, thanks.

> ---
>  hw/ppc/spapr.c |    8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 83c9d66dd56f..d6fd0e666e74 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3810,13 +3810,7 @@ static void spapr_pic_print_info(InterruptStatsProvider *obj,
>  
>  int spapr_get_vcpu_id(PowerPCCPU *cpu)
>  {
> -    CPUState *cs = CPU(cpu);
> -
> -    if (kvm_enabled()) {
> -        return kvm_arch_vcpu_id(cs);
> -    } else {
> -        return cs->cpu_index;
> -    }
> +    return cpu->vcpu_id;
>  }
>  
>  void spapr_set_vcpu_id(PowerPCCPU *cpu, int cpu_index, Error **errp)
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson