Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] pseries: fix TCG migration

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Tue, 2017-11-28 at 17:26 -0200, Daniel Henrique Barboza wrote:
> 
> On 11/28/2017 03:43 PM, Laurent Vivier wrote:
> > Migration of pseries is broken with TCG because
> > QEMU tries to restore KVM MMU state unconditionally.
> > 
> > The result is a SIGSEGV in kvm_vm_ioctl():
> > 
> >    #0  kvm_vm_ioctl (s=0x0, type=-2146390353)
> >        at qemu/accel/kvm/kvm-all.c:2032
> >    #1  0x00000001003e3e2c in kvmppc_configure_v3_mmu
> > (cpu=<optimized out>,
> >        radix=<optimized out>, gtse=<optimized out>,
> > proc_tbl=<optimized out>)
> >        at qemu/target/ppc/kvm.c:396
> >    #2  0x00000001002f8b88 in spapr_post_load (opaque=0x1019103c0,
> >        version_id=<optimized out>) at qemu/hw/ppc/spapr.c:1578
> >    #3  0x000000010059e4cc in vmstate_load_state (f=0x106230000,
> >        vmsd=0x1009479e0 <vmstate_spapr>, opaque=0x1019103c0,
> >        version_id=<optimized out>) at qemu/migration/vmstate.c:165
> >    #4  0x00000001005987e0 in vmstate_load (f=<optimized out>,
> > se=<optimized out>)
> >        at qemu/migration/savevm.c:748
> > 
> > This patch fixes the problem by not calling the KVM function with
> > the
> > TCG mode.
> > 
> > Fixes: d39c90f5f3 ("spapr: Fix migration of Radix guests")
> > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > ---
> > v2: fix the comment to keep GDB backtrace lines starting with '#'
> > 
> >   hw/ppc/spapr.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 9efddeaee5..a471de6cab 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1570,7 +1570,7 @@ static int spapr_post_load(void *opaque, int
> > version_id)
> >           err = spapr_rtc_import_offset(&spapr->rtc, spapr-
> > >rtc_offset);
> >       }
> > 
> > -    if (spapr->patb_entry) {
> > +    if (kvm_enabled() && spapr->patb_entry) {
> 
> As an alternative, I believe you can also do:
> 
> if (!!spapr->patb_entry) {
> 
> because the !! will return false if patb_entry is either undefined
> (as in

Hmmm, no. patb_entry is definately used in tcg

> TCG) or zero (as set in spapr_reallocate_hpt). This is the same logic
> used
> in spapr_patb_entry_needed too.
> 
> But I am fine with what you did and it's also clearer, so
> 
> 
> Reviewed-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
> 
> 
> 
> >           PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
> >           bool radix = !!(spapr->patb_entry & PATBE1_GR);
> >           bool gtse = !!(cpu->env.spr[SPR_LPCR] & LPCR_GTSE);
> 
>