linux-kernel - Re: [PATCH] KVM: nSVM: Enter guest mode before initializing nested NPT MMU

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Message-ID: <173958023279.1189000.15717835333610830974.b4-ty@google.com>
Date: Fri, 14 Feb 2025 16:50:07 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH] KVM: nSVM: Enter guest mode before initializing nested
 NPT MMU

On Wed, 29 Jan 2025 17:08:25 -0800, Sean Christopherson wrote:
> When preparing vmcb02 for nested VMRUN (or state restore), "enter" guest
> mode prior to initializing the MMU for nested NPT so that guest_mode is
> set in the MMU's role.  KVM's model is that all L2 MMUs are tagged with
> guest_mode, as the behavior of hypervisor MMUs tends to be significantly
> different than kernel MMUs.
> 
> Practically speaking, the bug is relatively benign, as KVM only directly
> queries role.guest_mode in kvm_mmu_free_guest_mode_roots(), which SVM
> doesn't use, and in paths that are optimizations (mmu_page_zap_pte() and
> shadow_mmu_try_split_huge_pages()).
> 
> [...]

Applied to kvm-x86 fixes, thanks!

[1/1] KVM: nSVM: Enter guest mode before initializing nested NPT MMU
      https://github.com/kvm-x86/linux/commit/46d6c6f3ef0e

--
https://github.com/kvm-x86/linux/tree/next