On Tue, 15 Aug 2017 11:40:34 +1000 Suraj Jitindar Singh <[email protected]> wrote:
> On Mon, 2017-08-14 at 19:49 +0200, Greg Kurz wrote: > > When running in KVM PR mode, kvmppc_set_compat() always fail because > > the > > current PR implementation doesn't handle KVM_REG_PPC_ARCH_COMPAT. Now > > that > > the machine code inconditionally calls ppc_set_compat_all() at reset > > time > > to restore the compat mode default value (commit 66d5c492dd3a9), it > > is > > impossible to start a guest with PR: > > > > qemu-system-ppc64: Unable to set CPU compatibility mode in KVM: > > Invalid argument > > > > A tentative patch [1] was recently sent by Suraj to address the > > issue, but > > it would prevent the compat mode to be turned off on reset. And we > > really > > don't want to explicitely check for KVM PR. During the patch's > > review, > > David suggested that we should only call the KVM ioctl() if the > > compat > > PVR changes. This allows at least to run with KVM PR, provided no > > compat > > mode is requested from the command line (which should be the case > > when > > running PR nested). This is what this patch does. > > > > While here, we also fix the side effect where KVM would fail but we > > would > > change the CPU state in QEMU anyway. > > > > [1] http://patchwork.ozlabs.org/patch/782039/ > > > > Signed-off-by: Greg Kurz <[email protected]> > > I meant to send a follow up but it fell on my priority list so thanks > for this > No problem :) This is more a workaround than an actual fix since CAS will still want to change the compat mode and fail, but at least QEMU doesn't exit right away. I needed that to chase down another bug that breaks loadvm of a KVM PR guest. > Looks good to me > > Reviewed-by: Suraj Jitindar Singh <[email protected]> > Thanks! > > --- > > target/ppc/compat.c | 9 +++++---- > > 1 file changed, 5 insertions(+), 4 deletions(-) > > > > diff --git a/target/ppc/compat.c b/target/ppc/compat.c > > index f1b67faa97e3..f8729fe46d61 100644 > > --- a/target/ppc/compat.c > > +++ b/target/ppc/compat.c > > @@ -140,16 +140,17 @@ void ppc_set_compat(PowerPCCPU *cpu, uint32_t > > compat_pvr, Error **errp) > > > > cpu_synchronize_state(CPU(cpu)); > > > > - cpu->compat_pvr = compat_pvr; > > - env->spr[SPR_PCR] = pcr & pcc->pcr_mask; > > - > > - if (kvm_enabled()) { > > + if (kvm_enabled() && cpu->compat_pvr != compat_pvr) { > > int ret = kvmppc_set_compat(cpu, cpu->compat_pvr); > > if (ret < 0) { > > error_setg_errno(errp, -ret, > > "Unable to set CPU compatibility mode > > in KVM"); > > + return; > > } > > } > > + > > + cpu->compat_pvr = compat_pvr; > > + env->spr[SPR_PCR] = pcr & pcc->pcr_mask; > > } > > > > typedef struct { > >
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