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AJvYcCWo9v5bltQJfUavaOy0TfbGUeMaG061BHpEk60FhY/5hrGQ6/sN/X5b3rRgd8MnqHi2t/I4D1GZHq1+UotP/3pQyQu65ryAFwbMlQMI X-Gm-Message-State: AOJu0Yz8FjorIo5OUhoLAkPjOS5QTrGxfjhTBKwKejqzqUeNryreMJed 9L/yro4kAYsHJYPL5Gd6x/NXm4aLm2Ad/AJNRi1ERQNYLt/V0nDj4OsFKwAFuz1SqaljwncwyEE lHw== X-Google-Smtp-Source: AGHT+IGWhkiIz2Y2g3Ner7BOHEwPH6Z/gYQ/jE0/y9L37RbGyZJn6Z1cRXZGPxQRndFfUlsvmeisfjj31Zs= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:903:2442:b0:1fa:13d8:a09c with SMTP id d9443c01a7336-1fbb6d601c4mr1788535ad.10.1720553286750; Tue, 09 Jul 2024 12:28:06 -0700 (PDT) Date: Tue, 9 Jul 2024 12:28:05 -0700 In-Reply-To: <924352564a5ab003b85bf7e2ee422907f9951e26.camel@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240517173926.965351-1-seanjc@google.com> <20240517173926.965351-34-seanjc@google.com> <924352564a5ab003b85bf7e2ee422907f9951e26.camel@redhat.com> Message-ID: Subject: Re: [PATCH v2 33/49] KVM: x86: Advertise TSC_DEADLINE_TIMER in KVM_GET_SUPPORTED_CPUID From: Sean Christopherson To: Maxim Levitsky Cc: Paolo Bonzini , Vitaly Kuznetsov , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Hou Wenlong , Kechen Lu , Oliver Upton , Binbin Wu , Yang Weijiang , Robert Hoo Content-Type: text/plain; charset="us-ascii" On Thu, Jul 04, 2024, Maxim Levitsky wrote: > On Fri, 2024-05-17 at 10:39 -0700, Sean Christopherson wrote: > > 4.47 KVM_PPC_GET_PVINFO > > ----------------------- > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > > index 699ce4261e9c..d1f427284ccc 100644 > > --- a/arch/x86/kvm/cpuid.c > > +++ b/arch/x86/kvm/cpuid.c > > @@ -680,8 +680,8 @@ void kvm_set_cpu_caps(void) > > F(FMA) | F(CX16) | 0 /* xTPR Update */ | F(PDCM) | > > F(PCID) | 0 /* Reserved, DCA */ | F(XMM4_1) | > > F(XMM4_2) | EMUL_F(X2APIC) | F(MOVBE) | F(POPCNT) | > > - 0 /* Reserved*/ | F(AES) | F(XSAVE) | 0 /* OSXSAVE */ | F(AVX) | > > - F(F16C) | F(RDRAND) > > + EMUL_F(TSC_DEADLINE_TIMER) | F(AES) | F(XSAVE) | > > + 0 /* OSXSAVE */ | F(AVX) | F(F16C) | F(RDRAND) > > ); > > > > kvm_cpu_cap_init(CPUID_1_EDX, > > Hi, > > I have a mixed feeling about this. > > First of all KVM_GET_SUPPORTED_CPUID documentation explicitly states that it > returns bits that are supported in *default* configuration TSC_DEADLINE_TIMER > and arguably X2APIC are only supported after enabling various caps, e.g not > default configuration. Another side topic, in the near future, I think we should push to make an in-kernel local APIC a hard requirement. AFAIK, userspace local APIC gets no meaningful test coverage, and IIRC we have known bugs where a userspace APIC doesn't work as it should, e.g. commit 6550c4df7e50 ("KVM: nVMX: Fix interrupt window request with "Acknowledge interrupt on exit""). > However, since X2APIC also in KVM_GET_SUPPORTED_CPUID (also wrongly IMHO), > for consistency it does make sense to add TSC_DEADLINE_TIMER as well. > > I do think that we need at least to update the documentation of KVM_GET_SUPPORTED_CPUID > and KVM_GET_EMULATED_CPUID, as I state in a review of a later patch. +1