Liang Yan <l...@digitalocean.com> writes:
> With cpu.pmu=off, perfctr_core could still be seen in an AMD guest cpuid.
> By further digging, I found cpu.perfctr_core did the trick. However,
> considering the 'enable_pmu' in KVM could work on both Intel and AMD,
> we may add AMD PMU control under 'enabe_pmu' in QEMU too.
>
> This change will overide the property 'perfctr_ctr' and change the AMD PMU
> to off by default.
>
> Signed-off-by: Liang Yan <l...@digtalocean.com>
> ---
> target/i386/cpu.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 22b681ca37..edf5413c90 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -5706,6 +5706,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> *ecx |= 1 << 1; /* CmpLegacy bit */
> }
> }
> +
> + if (!cpu->enable_pmu) {
> + *ecx &= ~CPUID_EXT3_PERFCORE;
> + }
> break;
> case 0x80000002:
> case 0x80000003:
I may be missing something but my first impression is that this will
make CPUID_EXT3_PERFCORE bit disappear when a !enable_pmu VM is migrated
from an old QEMU (pre-patch) to a new one. If so, then additional
precautions should be taking against that (e.g. tying the change to
CPU/machine model versions, for example).
--
Vitaly
