On Thu, Mar 30, 2017 at 01:28:36PM +1100, Sam Bobroff wrote: > On Wed, Mar 29, 2017 at 07:39:25AM +0200, Thomas Huth wrote: > > On 29.03.2017 07:01, Sam Bobroff wrote: > > > On Power8 hosts it is currently theoretically possible for QEMU/KVM-HV > > > guests > > > to receive a ibm,pa-features property indicating that HTM support is > > > available > > > when it is not. The situation would occur if the platform firmware of > > > a Power8 host cleared the HTM bit of the ibm,pa-features property. > > > > Out of curiosity: Is there a machine out there where this happens? > > Not that I know of... just the one who's firmware I broke on purpose for > testing ;-)
Ok, given that, I'm moving this fix from ppc-for-2.9 to ppc-for-2.10.
>
> > > QEMU would query KVM for the availability of HTM, which will return no
> > > support, but workaround code in kvm_arch_init_vcpu() would then
> > > re-enable it because KVM_HV is in use and the processor is P8.
> > >
> > > This patch adjusts the workaround in kvm_arch_init_vcpu() so that it does
> > > not
> > > enable HTM (in the above case) unless the host kernel indicates to the
> > > QEMU
> > > process, via the auxiliary vector, that userspace can use HTM (via the
> > > HWCAP2
> > > bit KVM_FEATURE2_HTM).
> > >
> > > The reason to use the value from the auxiliary vector is that it is
> > > set based only on what the host kernel found in the ibm,pa-features
> > > HTM bit at boot time.
> > >
> > > Signed-off-by: Sam Bobroff <sam.bobr...@au1.ibm.com>
> > > ---
> > > target/ppc/kvm.c | 8 ++++++--
> > > 1 file changed, 6 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> > > index 9f1f132cef..8a54709ae4 100644
> > > --- a/target/ppc/kvm.c
> > > +++ b/target/ppc/kvm.c
> > > @@ -49,6 +49,7 @@
> > > #if defined(TARGET_PPC64)
> > > #include "hw/ppc/spapr_cpu_core.h"
> > > #endif
> > > +#include "elf.h"
> > >
> > > //#define DEBUG_KVM
> > >
> > > @@ -509,8 +510,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
> > > case POWERPC_MMU_2_07:
> > > if (!cap_htm && !kvmppc_is_pr(cs->kvm_state)) {
> > > /* KVM-HV has transactional memory on POWER8 also without the
> > > - * KVM_CAP_PPC_HTM extension, so enable it here instead. */
> > > - cap_htm = true;
> > > + * KVM_CAP_PPC_HTM extension, so enable it here instead as
> > > + * long as it's availble to userspace on the host. */
> > > + if (qemu_getauxval(AT_HWCAP2) & PPC_FEATURE2_HAS_HTM) {
> > > + cap_htm = true;
> > > + }
> >
> > That's a very good idea! ... but I think you could also merge the two
> > if-statements into one to save one level of indentation.
> >
> > Thomas
>
--
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
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