Re: [PATCH] KVM: PPC: powerpc: Add count cache flush parameters to kvmppc_get_cpu_char()

Michael Ellerman
2019-03-03T09:06:29Z

Paul Mackerras <paulus@ozlabs.org> writes:

> On Fri, Mar 01, 2019 at 05:52:51PM +1100, Michael Ellerman wrote:
>> Suraj Jitindar Singh <sjitindarsingh@gmail.com> writes:
>>
>> > Add KVM_PPC_CPU_CHAR_BCCTR_FLUSH_ASSIST &
>> > KVM_PPC_CPU_BEHAV_FLUSH_COUNT_CACHE to the characteristics returned from
>> > the H_GET_CPU_CHARACTERISTICS H-CALL, as queried from either the
>> > hypervisor or the device tree.
>> >
>> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
>> > ---
>> > arch/powerpc/include/uapi/asm/kvm.h | 2 ++
>> > arch/powerpc/kvm/powerpc.c | 18 ++++++++++++++----
>> > 2 files changed, 16 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> > index b90a7d154180..a99dcac91e50 100644
>> > --- a/arch/powerpc/kvm/powerpc.c
>> > +++ b/arch/powerpc/kvm/powerpc.c
>> > @@ -2251,12 +2253,16 @@ static int kvmppc_get_cpu_char(struct kvm_ppc_cpu_char *cp)
>> > if (have_fw_feat(fw_features, "enabled",
>> > "fw-count-cache-disabled"))
>> > cp->character |= KVM_PPC_CPU_CHAR_COUNT_CACHE_DIS;
>> > + if (have_fw_feat(fw_features, "enabled",
>> > + "fw-count-cache-flush-bcctr2,0,0"))
>>
>> I don't think there's any reason KVM needs to be querying the device
>> tree directly, is there?
>>
>> Can't it just use the security flags (security_features.h), that are
>> initialised by the powernv platform code based on the device tree.
>
> My recollection is that the security flags didn't have all the
> information we need. It's possible that's no longer true.

Actually I don't think they existed at all back then, we didn't add them
until after the initial panic.

> I merged the patch and sent a pull request to Paolo; using the same
> pattern as the existing code made it a low-risk patch and I wanted to
> get it in for 5.1. For 5.2 we can look at changing it over if you
> like.

Yep that's fine.

cheers