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Wed, 13 May 2026 11:51:32 -0400 X-MC-Unique: n3xU9EYmPtu9hcHD57-Bgw-1 X-Mimecast-MFC-AGG-ID: n3xU9EYmPtu9hcHD57-Bgw_1778687491 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0ED5C18002C8; Wed, 13 May 2026 15:51:31 +0000 (UTC) Received: from [10.44.50.86] (unknown [10.44.50.86]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 8E44C180058F; Wed, 13 May 2026 15:51:29 +0000 (UTC) Message-ID: Date: Wed, 13 May 2026 17:51:28 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: VMX: introduce module parameter to disable CET To: Sean Christopherson Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, David Riley References: <20260512150016.2979228-1-pbonzini@redhat.com> Content-Language: en-US From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 5/13/26 01:55, Sean Christopherson wrote: > On Tue, May 12, 2026, Paolo Bonzini wrote: >> There have been reports of host hangs caused by CET virtualization. >> Until these are analyzed further, introduce a module parameter that >> makes it possible to easily disable it. >> >> Link: https://lore.kernel.org/all/85548beb-1486-40f9-beb4-632c78e3360b@proxmox.com/ >> Cc: David Riley >> Signed-off-by: Paolo Bonzini >> --- >> arch/x86/kvm/vmx/capabilities.h | 1 + >> arch/x86/kvm/vmx/vmcs12.c | 2 +- >> arch/x86/kvm/vmx/vmx.c | 17 +++++++++++++++-- >> 3 files changed, 17 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h >> index 56cacc06225e..31568274d8bb 100644 >> --- a/arch/x86/kvm/vmx/capabilities.h >> +++ b/arch/x86/kvm/vmx/capabilities.h >> @@ -14,6 +14,7 @@ extern bool __read_mostly flexpriority_enabled; >> extern bool __read_mostly enable_ept; >> extern bool __read_mostly enable_unrestricted_guest; >> extern bool __read_mostly enable_ept_ad_bits; >> +extern bool __read_mostly enable_cet; >> extern bool __read_mostly enable_pml; >> extern int __read_mostly pt_mode; >> >> diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c >> index 1ebe67c384ad..9f96e21dc1b9 100644 >> --- a/arch/x86/kvm/vmx/vmcs12.c >> +++ b/arch/x86/kvm/vmx/vmcs12.c >> @@ -202,7 +202,7 @@ static __init bool cpu_has_vmcs12_field(unsigned int idx) >> case HOST_S_CET: >> case HOST_SSP: >> case HOST_INTR_SSP_TABLE: >> - return cpu_has_load_cet_ctrl(); >> + return enable_cet; > > As implemented, cpu_has_vmcs12_field() checks raw CPU support, not what KVM is > using. E.g. EPT_POINTER checks cpu_has_vmx_ept(), not enable_ept. Whether or > not that's ideal/desirable, dunno. But I think we should at least be consistent. > > An alternative approach would be to squash the controls themselves. Though again, > I'd probably only want to do that if we plan on taking that approach for all such > module params. Yes, that was my first idea but it's not great to do it inconsistently. I'll remove the cpu_has_vmcs12_field() hunk though. Paolo