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KVM: x86: Ignore CR0.WP toggles in non-paging mode

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If paging is disabled, there are no permission bits to emulate.
Micro-optimize this case to avoid unnecessary work.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230322013731.102955-4-minipli@grsecurity.net
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Mathias Krause
2023-03-22 02:37:28 +01:00
committed by Sean Christopherson
parent 01b31714bd
commit e40bcf9f3a
1 changed files with 13 additions and 7 deletions
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arch/x86/kvm/x86.c
+13 -7
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@@ -908,14 +908,20 @@ void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned lon
{
/*
* CR0.WP is incorporated into the MMU role, but only for non-nested,
* indirect shadow MMUs. If TDP is enabled, the MMU's metadata needs
* to be updated, e.g. so that emulating guest translations does the
* right thing, but there's no need to unload the root as CR0.WP
* doesn't affect SPTEs.
* indirect shadow MMUs. If paging is disabled, no updates are needed
* as there are no permission bits to emulate. If TDP is enabled, the
* MMU's metadata needs to be updated, e.g. so that emulating guest
* translations does the right thing, but there's no need to unload the
* root as CR0.WP doesn't affect SPTEs.
*/
if (tdp_enabled && (cr0 ^ old_cr0) == X86_CR0_WP) {
kvm_init_mmu(vcpu);
return;
if ((cr0 ^ old_cr0) == X86_CR0_WP) {
if (!(cr0 & X86_CR0_PG))
return;
if (tdp_enabled) {
kvm_init_mmu(vcpu);
return;
}
}
if ((cr0 ^ old_cr0) & X86_CR0_PG) {