From: Paolo Bonzini <pbonzini@redhat.com>
To: Jim Mattson <jmattson@google.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
"Xu, Like" <like.xu@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Like Xu <like.xu@linux.intel.com>
Subject: Re: [PATCH] KVM: VMX: Always treat MSR_IA32_PERF_CAPABILITIES as a valid PMU MSR
Date: Thu, 4 Jun 2020 18:49:44 +0200 [thread overview]
Message-ID: <285863c6-ef4b-a6f0-d223-ebc7cc515f84@redhat.com> (raw)
In-Reply-To: <CALMp9eQoKJg36AabLErekJ-U10-DkRHW=dn14q0bxQHh7XrGMQ@mail.gmail.com>
On 04/06/20 18:44, Jim Mattson wrote:
>>> I don't know if I would call it a "good assumption" so much as a "necessary
>>> assumption". KVM_{GET,SET}_MSRS are allowed, and must function correctly,
>>> if they're called prior to KVM_SET_CPUID{2}.
>> Generally speaking this is not the case for the PMU; get_gp_pmc for
>> example depends on pmu->nr_arch_gp_counters which is initialized based
>> on CPUID leaf 0xA.
>>
>> The assumption that this patch fixes is that you can blindly take the
>> output of KVM_GET_MSR_INDEX_LIST and pass it to KVM_{GET,SET}_MSRS.
>
> Is that an assumption or an invariant?
Both, I guess (a valid assumption for userspace, an invariant to be
respected for the kernel code).
The part where we don't fare to well, is that a bunch of MSRs that need
save/restore are _not_ included in KVM_GET_MSR_INDEX_LIST (and the PMU
is the biggest if not the only offender there).
Paolo
prev parent reply other threads:[~2020-06-04 16:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-03 20:33 Sean Christopherson
2020-06-04 1:37 ` Xu, Like
2020-06-04 15:16 ` Sean Christopherson
2020-06-04 16:20 ` Paolo Bonzini
2020-06-04 16:44 ` Jim Mattson
2020-06-04 16:49 ` Paolo Bonzini [this message]
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