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Re: [Qemu-ppc] [PATCH 1/1] target/ppc: Improve accuracy of guest HTM ava
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [PATCH 1/1] target/ppc: Improve accuracy of guest HTM availability on P8s |
Date: |
Wed, 29 Mar 2017 16:23:11 +1100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Wed, Mar 29, 2017 at 04:01:28PM +1100, 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.
> 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 <address@hidden>
Applied to ppc-for-2.9.
> ---
> 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;
> + }
> }
> break;
> default:
--
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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