From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 66FAE2107; Tue, 29 Oct 2024 17:40:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730223651; cv=none; b=tX3/AWfhI9f2ElciqjNOpZX+wRLSMVfaDuaQhMFfKmfJYB8wvYcXXl7Tv5PuN1xGPYIrnJN480J6XxhJ55U5AjtAgLXqbMeobLeuiipgdYPS33jikJpmZLkAJtlda0BCy+NjBIUBSRMwKyGeajUhinyCh7NjfQT1OCXb8HkYrYU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730223651; c=relaxed/simple; bh=nOaHu/IehEL6OQiLLzh5zQdYlqOfd77xgDIYOg4DnAo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uiVu1IeFlnaGi2enyIU/OKZbZzrYravHgANnWMP7wUqRA0g54cZ0jdnTi1zmPSEtKlTMU3gj95mjMHqJWLhqWy2M1OT2GFg0FOWu7pwPzgzvBa4wIgI/kBOVaj+3KyURikYp6iOnY+e8bQM70MDdDOELd311ndls6DFrRro7LS0= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=prWlFthlScSlGElGCx1KOSTF9/+bR6IBrIn8zROURZ5GpR4+/Zk6ti2sYv2aB51+q HHVlYD85bN5u0dbpR9sNp/BA3UPvMJvN3/SHrVSZo8GM6HgdU7V92S5C04ByVEFS4a BX76o/UpzVfQPaLSFvo5M2l8NnsMtRt7ZhtLnPX2TbZrGJdoqqL+JSp9S1ZVk5r3P2 /L1x8K52qb0lsshahMxfSv1dgjPVZx0/gSSVzd+rDgG/S68izOfhu+FZ+b34obl1mV dEOG8vkad6Q0JdH7jyNB3jFeZhw745r8bwrYm1G7qOHUjtJZuzqryj6CA4I1lyoEoQ OFq5kEREnpMcw== Message-ID: <538c630c-0de3-4807-9e9f-6af02dd18d0e@zytor.com> Date: Tue, 29 Oct 2024 10:40:03 -0700 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 25/27] KVM: nVMX: Add FRED VMCS fields To: Sean Christopherson , Chao Gao Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, pbonzini@redhat.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, andrew.cooper3@citrix.com References: <20241001050110.3643764-1-xin@zytor.com> <20241001050110.3643764-26-xin@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/28/2024 11:27 AM, Sean Christopherson wrote: > On Mon, Oct 28, 2024, Chao Gao wrote: >> On Fri, Oct 25, 2024 at 12:25:45AM -0700, Xin Li wrote: >>>>> static void nested_vmx_setup_cr_fixed(struct nested_vmx_msrs *msrs) >>>>> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h >>>>> index 2c296b6abb8c..5272f617fcef 100644 >>>>> --- a/arch/x86/kvm/vmx/nested.h >>>>> +++ b/arch/x86/kvm/vmx/nested.h >>>>> @@ -251,6 +251,14 @@ static inline bool nested_cpu_has_encls_exit(struct vmcs12 *vmcs12) >>>>> return nested_cpu_has2(vmcs12, SECONDARY_EXEC_ENCLS_EXITING); >>>>> } >>>>> >>>>> +static inline bool nested_cpu_has_fred(struct vmcs12 *vmcs12) >>>>> +{ >>>>> + return vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_FRED && >>>>> + vmcs12->vm_exit_controls & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS && >>>>> + vmcs12->secondary_vm_exit_controls & SECONDARY_VM_EXIT_SAVE_IA32_FRED && >>>>> + vmcs12->secondary_vm_exit_controls & SECONDARY_VM_EXIT_LOAD_IA32_FRED; >>>> >>>> Is it a requirement in the SDM that the VMM should enable all FRED controls or >>>> none? If not, the VMM is allowed to enable only one or two of them. This means >>>> KVM would need to emulate FRED controls for the L1 VMM as three separate >>>> features. >>> >>> The SDM doesn't say that. But FRED states are used during and >>> immediately after VM entry and exit, I don't see a good reason for a VMM >>> to enable only one or two of the 3 save/load configs. > > Not KVM's concern. > >>> Say if VM_ENTRY_LOAD_IA32_FRED is not set, it means a VMM needs to >>> switch to guest FRED states before it does a VM entry, which is >>> absolutely a big mess. > > Again, not KVM's concern. > >> If the VMM doesn't enable FRED, it's fine to load guest FRED states before VM >> entry, right? > > Yep. Or if L1 is simply broken and elects to manually load FRED state before > VM-Enter instead of using VM_ENTRY_LOAD_IA32_FRED, then any badness that happens > is 100% L1's problem to deal with. KVM's responsiblity is to emulate the > architectural behavior, what L1 may or may not do is irrelevant. Damn, obviously I COMPLETELY missed this point. Let me think how should KVM as L0 handle it. > >> The key is to emulate hardware behavior accurately without making assumptions >> about guests. > > +1000 > >> If some combinations of controls cannot be emulated properly, KVM >> should report internal errors at some point. Yeah, only if CANNOT. Otherwise a broken VMM will behave differently on real hardware and KVM, even if it crashes in a way which it never knows about, right?