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Fri, 08 Nov 2024 01:08:00 -0800 (PST) X-Google-Smtp-Source: AGHT+IGGUvT8AVR9wC5DZNJzYXbfHT1WEe0sZH4euqeeNl3BRR3mGOctibneYjQL/yXyjBjT68UOUQ== X-Received: by 2002:a05:600c:a42:b0:42f:8fcd:486c with SMTP id 5b1f17b1804b1-432b751f5f8mr14619965e9.33.1731056880222; Fri, 08 Nov 2024 01:08:00 -0800 (PST) Received: from [192.168.10.47] ([151.49.84.243]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-381ed97ce27sm3968972f8f.29.2024.11.08.01.07.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Nov 2024 01:07:59 -0800 (PST) Message-ID: Date: Fri, 8 Nov 2024 10:07:58 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] KVM: VMX: Bury Intel PT virtualization (guest/host mode) behind CONFIG_BROKEN To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Adrian Hunter References: <20241101185031.1799556-1-seanjc@google.com> <20241101185031.1799556-2-seanjc@google.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/1/24 19:50, Sean Christopherson wrote: > Hide KVM's pt_mode module param behind CONFIG_BROKEN, i.e. disable support > for virtualizing Intel PT via guest/host mode unless BROKEN=y. There are > myriad bugs in the implementation, some of which are fatal to the guest, > and others which put the stability and health of the host at risk. > > For guest fatalities, the most glaring issue is that KVM fails to ensure > tracing is disabled, and *stays* disabled prior to VM-Enter, which is > necessary as hardware disallows loading (the guest's) RTIT_CTL if tracing > is enabled (enforced via a VMX consistency check). Per the SDM: > > If the logical processor is operating with Intel PT enabled (if > IA32_RTIT_CTL.TraceEn = 1) at the time of VM entry, the "load > IA32_RTIT_CTL" VM-entry control must be 0. > > On the host side, KVM doesn't validate the guest CPUID configuration > provided by userspace, and even worse, uses the guest configuration to > decide what MSRs to save/load at VM-Enter and VM-Exit. E.g. configuring > guest CPUID to enumerate more address ranges than are supported in hardware > will result in KVM trying to passthrough, save, and load non-existent MSRs, > which generates a variety of WARNs, ToPA ERRORs in the host, a potential > deadlock, etc. > > Fixes: f99e3daf94ff ("KVM: x86: Add Intel PT virtualization work mode") > Cc: stable@vger.kernel.org > Cc: Adrian Hunter > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/vmx/vmx.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 6ed801ffe33f..087504fb1589 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -217,9 +217,11 @@ module_param(ple_window_shrink, uint, 0444); > static unsigned int ple_window_max = KVM_VMX_DEFAULT_PLE_WINDOW_MAX; > module_param(ple_window_max, uint, 0444); > > -/* Default is SYSTEM mode, 1 for host-guest mode */ > +/* Default is SYSTEM mode, 1 for host-guest mode (which is BROKEN) */ > int __read_mostly pt_mode = PT_MODE_SYSTEM; > +#ifdef CONFIG_BROKEN > module_param(pt_mode, int, S_IRUGO); > +#endif > > struct x86_pmu_lbr __ro_after_init vmx_lbr_caps; > Applied, thanks. Paolo