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Date: Tue, 10 Aug 2021 11:23:48 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Jim Mattson <jmattson@...gle.com>, Sean Christopherson <seanjc@...gle.com> Cc: Yu Zhang <yu.c.zhang@...ux.intel.com>, Wei Huang <wei.huang2@....com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, vkuznets@...hat.com, wanpengli@...cent.com, joro@...tes.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com Subject: Re: [PATCH v2 1/3] KVM: x86: Allow CPU to force vendor-specific TDP level On 09/08/21 23:49, Jim Mattson wrote: > Doesn't this break legacy type 2 hypervisors that don't know anything > about 5-level NPT and don't have any control over whether or not the > host uses 5-level paging? Yes, where "legacy" probably means "all released versions of all of them", including KVM. Host support for LA57 was merged in 4.13, while KVM started supporting 5-level page tables in EPT in 4.14 and even then just returned PT64_ROOT_LEVEL (i.e. 4) for the maximum NPT level. So all Linux versions up to 5.13, which has "KVM: x86: Prevent KVM SVM from loading on kernels with 5-level paging", will break horribly. Better backport that patch to stable... Paolo
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