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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id k3sm37677056pgq.54.2022.01.05.13.09.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Jan 2022 13:09:16 -0800 (PST) Date: Wed, 5 Jan 2022 21:09:13 +0000 From: Sean Christopherson To: Like Xu Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND] KVM: x86/pmu: Make top-down.slots event unavailable in supported leaf Message-ID: References: <20220105050711.67280-1-likexu@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220105050711.67280-1-likexu@tencent.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Jan 05, 2022, Like Xu wrote: > From: Like Xu > > When we choose to disable the fourth fixed counter TOPDOWN.SLOTS, > we need to also reduce the length of the 0AH.EBX bit vector, which > enumerates architecture performance monitoring events, and set > 0AH.EBX.[bit 7] to 1 if the new value of EAX[31:24] is still > 7. > > Fixes: 2e8cd7a3b8287 ("kvm: x86: limit the maximum number of vPMU fixed counters to 3") > Signed-off-by: Like Xu > --- > arch/x86/kvm/cpuid.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 0b920e12bb6d..1f0131145296 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -782,6 +782,21 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > eax.split.mask_length = cap.events_mask_len; > > edx.split.num_counters_fixed = min(cap.num_counters_fixed, MAX_FIXED_COUNTERS); > + > + /* > + * The 8th Intel pre-defined architectural event (Topdown Slots) will be supported > + * if the 4th fixed counter exists && EAX[31:24] > 7 && EBX[7] = 0. Please wrap at ~80 chars. > + * > + * Currently, KVM needs to set EAX[31:24] < 8 or EBX[7] == 1 > + * to make this event unavailable in a consistent way. > + */ > + if (edx.split.num_counters_fixed < 4) { > + if (eax.split.mask_length > 7) > + eax.split.mask_length--; This will break if there's a bit>7 enumerated in EBX (events_mask) that KVM wants to expose to the guest. It doesn't cause problems today because bits 31:8 are all reserved, but that will not always be the case. We could do if (edx.split.num_counters_fixed < 4) { if (eax.split.mask_length == 7) eax.split.mask_length--; else cap.events_mask |= BIT_ULL(7); } but I don't see any reason to make this more complex than: if (edx.split.num_counters_fixed < 4 && eax.split.mask_length > 7) cap.events_mask |= BIT_ULL(7); > + if (eax.split.mask_length > 7) > + cap.events_mask |= BIT_ULL(7); > + } > + > edx.split.bit_width_fixed = cap.bit_width_fixed; > if (cap.version) > edx.split.anythread_deprecated = 1; > -- > 2.33.1 >