From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57444) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ct6KV-0005Vr-8F for qemu-devel@nongnu.org; Wed, 29 Mar 2017 01:39:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ct6KS-00067m-6R for qemu-devel@nongnu.org; Wed, 29 Mar 2017 01:39:35 -0400 References: From: Thomas Huth Message-ID: <516d1e19-8506-1ae6-f923-55abd9fe6722@redhat.com> Date: Wed, 29 Mar 2017 07:39:25 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] target/ppc: Improve accuracy of guest HTM availability on P8s List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Sam Bobroff , qemu-devel@nongnu.org Cc: qemu-ppc@nongnu.org, david@gibson.dropbear.id.au 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? > 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 > --- > 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