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

[Daniel Henrique Barboza]

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 <address@hidden>
> ---
> 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
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 <address@hidden>



>           PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
>           bool radix = !!(spapr->patb_entry & PATBE1_GR);
>           bool gtse = !!(cpu->env.spr[SPR_LPCR] & LPCR_GTSE);