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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id y6-20020a5d6206000000b0021350f7b22esm20581038wru.109.2022.06.22.02.39.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jun 2022 02:39:45 -0700 (PDT) From: Vitaly Kuznetsov To: Paul Durrant Cc: Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present In-Reply-To: <20220622092202.15548-1-pdurrant@amazon.com> References: <20220622092202.15548-1-pdurrant@amazon.com> Date: Wed, 22 Jun 2022 11:39:44 +0200 Message-ID: <87wnd9xcin.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul Durrant writes: > The scaling information in sub-leaf 1 should match the values in the > 'vcpu_info' sub-structure 'time_info' (a.k.a. pvclock_vcpu_time_info) which > is shared with the guest. The offset values are not set since a TSC offset > is already applied. > The host TSC frequency should also be set in sub-leaf 2. > > This patch adds a new kvm_xen_set_cpuid() function that scans for the > relevant CPUID leaf when the CPUID information is updated by the VMM and > stashes pointers to the sub-leaves in the kvm_vcpu_xen structure. > The values are then updated by a call to the, also new, > kvm_xen_setup_tsc_info() function made at the end of > kvm_guest_time_update() just before entering the guest. > > Signed-off-by: Paul Durrant > --- > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/cpuid.c | 2 ++ > arch/x86/kvm/x86.c | 1 + > arch/x86/kvm/xen.c | 41 +++++++++++++++++++++++++++++++++ > arch/x86/kvm/xen.h | 10 ++++++++ > 5 files changed, 56 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 1038ccb7056a..f77a4940542f 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -638,6 +638,8 @@ struct kvm_vcpu_xen { > struct hrtimer timer; > int poll_evtchn; > struct timer_list poll_timer; > + struct kvm_cpuid_entry2 *tsc_info_1; > + struct kvm_cpuid_entry2 *tsc_info_2; > }; > > struct kvm_vcpu_arch { > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index d47222ab8e6e..eb6cd88c974a 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -25,6 +25,7 @@ > #include "mmu.h" > #include "trace.h" > #include "pmu.h" > +#include "xen.h" > > /* > * Unlike "struct cpuinfo_x86.x86_capability", kvm_cpu_caps doesn't need to be > @@ -310,6 +311,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu) > __cr4_reserved_bits(guest_cpuid_has, vcpu); > > kvm_hv_set_cpuid(vcpu); > + kvm_xen_set_cpuid(vcpu); > > /* Invoke the vendor callback only after the above state is updated. */ > static_call(kvm_x86_vcpu_after_set_cpuid)(vcpu); > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 00e23dc518e0..8b45f9975e45 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3123,6 +3123,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > if (vcpu->xen.vcpu_time_info_cache.active) > kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0); > kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); > + kvm_xen_setup_tsc_info(v); > return 0; > } > > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > index 610beba35907..a016ff85264d 100644 > --- a/arch/x86/kvm/xen.c > +++ b/arch/x86/kvm/xen.c > @@ -10,6 +10,9 @@ > #include "xen.h" > #include "hyperv.h" > #include "lapic.h" > +#include "cpuid.h" > + > +#include > > #include > #include > @@ -1855,3 +1858,41 @@ void kvm_xen_destroy_vm(struct kvm *kvm) > if (kvm->arch.xen_hvm_config.msr) > static_branch_slow_dec_deferred(&kvm_xen_enabled); > } > + > +void kvm_xen_set_cpuid(struct kvm_vcpu *vcpu) > +{ > + u32 base = 0; > + u32 function; > + > + for_each_possible_hypervisor_cpuid_base(function) { > + struct kvm_cpuid_entry2 *entry = kvm_find_cpuid_entry(vcpu, function, 0); > + > + if (entry && > + entry->ebx == XEN_CPUID_SIGNATURE_EBX && > + entry->ecx == XEN_CPUID_SIGNATURE_ECX && > + entry->edx == XEN_CPUID_SIGNATURE_EDX) { > + base = function; > + break; > + } > + } > + if (!base) > + return; > + > + function = base | XEN_CPUID_LEAF(3); > + vcpu->arch.xen.tsc_info_1 = kvm_find_cpuid_entry(vcpu, function, 1); > + vcpu->arch.xen.tsc_info_2 = kvm_find_cpuid_entry(vcpu, function, 2); > +} Imagine the following scenario: CPUID data was supplied with Xen CPUID leaves first and then got updated with new information which doesn't have Xen CPUID info (e.g. has Hyper-V signature instead of Xen in the same 0x40000000 leaf). Won't arch.xen.tsc_info_1/arch.xen.tsc_info_2 pointers become dangling here after we free the old CPUID data ... > + > +void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu) > +{ > + struct kvm_cpuid_entry2 *entry = vcpu->arch.xen.tsc_info_1; > + > + if (entry) { > + entry->ecx = vcpu->arch.hv_clock.tsc_to_system_mul; > + entry->edx = vcpu->arch.hv_clock.tsc_shift; ... just to crash everything here? > + } > + > + entry = vcpu->arch.xen.tsc_info_2; > + if (entry) > + entry->eax = vcpu->arch.hw_tsc_khz; > +} > diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h > index 532a535a9e99..1afb663318a9 100644 > --- a/arch/x86/kvm/xen.h > +++ b/arch/x86/kvm/xen.h > @@ -32,6 +32,8 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe, > int kvm_xen_setup_evtchn(struct kvm *kvm, > struct kvm_kernel_irq_routing_entry *e, > const struct kvm_irq_routing_entry *ue); > +void kvm_xen_set_cpuid(struct kvm_vcpu *vcpu); > +void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu); > > static inline bool kvm_xen_msr_enabled(struct kvm *kvm) > { > @@ -135,6 +137,14 @@ static inline bool kvm_xen_timer_enabled(struct kvm_vcpu *vcpu) > { > return false; > } > + > +static inline void kvm_xen_set_cpuid(struct kvm_vcpu *vcpu) > +{ > +} > + > +static inline void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu) > +{ > +} > #endif > > int kvm_xen_hypercall(struct kvm_vcpu *vcpu); -- Vitaly