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KVM: nSVM: Only copy SVM_MISC_ENABLE_NP from VMCB01's misc_ctl

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The 'misc_ctl' field in VMCB02 is taken as-is from VMCB01. However, the
only bit that needs to copied is SVM_MISC_ENABLE_NP, as all other known
bits in misc_ctl are related to SEV guests, and KVM doesn't support
nested virtualization for SEV guests.

Only copy SVM_MISC_ENABLE_NP to harden against future bugs if/when other
bits are set for L1 but should not be set for L2.

Opportunistically add a comment explaining why SVM_MISC_ENABLE_NP is
taken from VMCB01 and not VMCB02.

Suggested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260303003421.2185681-26-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Yosry Ahmed 2026-03-03 00:34:19 +00:00 committed by Sean Christopherson
parent c8123e8272
commit b6dc21d896
1 changed files with 10 additions and 2 deletions
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12
arch/x86/kvm/svm/nested.c
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@ -837,8 +837,16 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
V_NMI_BLOCKING_MASK);
}
/* Copied from vmcb01. msrpm_base can be overwritten later. */
vmcb02->control.misc_ctl = vmcb01->control.misc_ctl;
/*
* Copied from vmcb01. msrpm_base can be overwritten later.
*
* SVM_MISC_ENABLE_NP in vmcb12 is only used for consistency checks. If
* L1 enables NPTs, KVM shadows L1's NPTs and uses those to run L2. If
* L1 disables NPT, KVM runs L2 with the same NPTs used to run L1. For
* the latter, L1 runs L2 with shadow page tables that translate L2 GVAs
* to L1 GPAs, so the same NPTs can be used for L1 and L2.
*/
vmcb02->control.misc_ctl = vmcb01->control.misc_ctl & SVM_MISC_ENABLE_NP;
vmcb02->control.iopm_base_pa = vmcb01->control.iopm_base_pa;
vmcb02->control.msrpm_base_pa = vmcb01->control.msrpm_base_pa;
vmcb_mark_dirty(vmcb02, VMCB_PERM_MAP);