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From: | Xiaoyao Li |
Subject: | Re: [PATCH v1 00/40] TDX QEMU support |
Date: | Tue, 2 Aug 2022 18:55:48 +0800 |
User-agent: | Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0 Thunderbird/91.11.0 |
On 8/2/2022 5:49 PM, Daniel P. Berrangé wrote:
On Tue, Aug 02, 2022 at 03:47:10PM +0800, Xiaoyao Li wrote:
- CPU model We cannot create a TD with arbitrary CPU model like what for non-TDX VMs, because only a subset of features can be configured for TD.- It's recommended to use '-cpu host' to create TD;- '+feature/-feature' might not work as expected; future work: To introduce specific CPU model for TDs and enhance +/-features for TDs.Which features are incompatible with TDX ?
TDX enforces some features fixed to 1 (e.g., CPUID_EXT_X2APIC, CPUID_EXT_HYPERVISOR)and some fixed to 0 (e.g., CPUID_EXT_VMX ).
Details can be found in patch 8 and TDX spec chapter "CPUID virtualization"
Presumably you have such a list, so that KVM can block them whenusing '-cpu host' ?
No, KVM doesn't do this. The result is no error reported from KVM but what TD OS sees from CPUID might be different what user specifies in QEMU.
If so, we should be able to sanity check the use of these features in QEMU for the named CPU models / feature selection too.
This series enhances get_supported_cpuid() for TDX. If named CPU models are used to boot a TDX guest, it likely gets warning of "xxx feature is not available"
We have another series to enhance the "-feature" for TDX, to warn out if some fixed1 is specified to be removed. Besides, we will introduce specific named CPU model for TDX. e.g., TDX-SapphireRapids which contains the maximum feature set a TDX guest can have on SPR host.
With regards, Daniel
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