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authorSean Christopherson <seanjc@google.com>2021-08-23 17:58:24 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2021-09-06 05:56:38 -0400
commita717a780fc4e1dddd3fbf9ad08f180eec2a78194 (patch)
tree7eeb7a6e4ffb8e8686152dcb91d1ff88f4721a11 /arch/x86/kvm
parent43e540cc9f2ca12a2364ddf64e5ef929a546550d (diff)
downloadlinux-a717a780fc4e1dddd3fbf9ad08f180eec2a78194.tar.bz2
KVM: x86/mmu: Don't freak out if pml5_root is NULL on 4-level host
Include pml5_root in the set of special roots if and only if the host, and thus NPT, is using 5-level paging. mmu_alloc_special_roots() expects special roots to be allocated as a bundle, i.e. they're either all valid or all NULL. But for pml5_root, that expectation only holds true if the host uses 5-level paging, which causes KVM to WARN about pml5_root being NULL when the other special roots are valid. The silver lining of 4-level vs. 5-level NPT being tied to the host kernel's paging level is that KVM's shadow root level is constant; unlike VMX's EPT, KVM can't choose 4-level NPT based on guest.MAXPHYADDR. That means KVM can still expect pml5_root to be bundled with the other special roots, it just needs to be conditioned on the shadow root level. Fixes: cb0f722aff6e ("KVM: x86/mmu: Support shadowing NPT when 5-level paging is enabled in host") Reported-by: Maxim Levitsky <mlevitsk@redhat.com> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210824005824.205536-1-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r--arch/x86/kvm/mmu/mmu.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c04e30f6e0db..e7bac871747c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3588,6 +3588,7 @@ out_unlock:
static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
{
struct kvm_mmu *mmu = vcpu->arch.mmu;
+ bool need_pml5 = mmu->shadow_root_level > PT64_ROOT_4LEVEL;
u64 *pml5_root = NULL;
u64 *pml4_root = NULL;
u64 *pae_root;
@@ -3602,7 +3603,14 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
mmu->shadow_root_level < PT64_ROOT_4LEVEL)
return 0;
- if (mmu->pae_root && mmu->pml4_root && mmu->pml5_root)
+ /*
+ * NPT, the only paging mode that uses this horror, uses a fixed number
+ * of levels for the shadow page tables, e.g. all MMUs are 4-level or
+ * all MMus are 5-level. Thus, this can safely require that pml5_root
+ * is allocated if the other roots are valid and pml5 is needed, as any
+ * prior MMU would also have required pml5.
+ */
+ if (mmu->pae_root && mmu->pml4_root && (!need_pml5 || mmu->pml5_root))
return 0;
/*
@@ -3610,7 +3618,7 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
* bail if KVM ends up in a state where only one of the roots is valid.
*/
if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->pml4_root ||
- mmu->pml5_root))
+ (need_pml5 && mmu->pml5_root)))
return -EIO;
/*
@@ -3626,7 +3634,7 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu)
if (!pml4_root)
goto err_pml4;
- if (mmu->shadow_root_level > PT64_ROOT_4LEVEL) {
+ if (need_pml5) {
pml5_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
if (!pml5_root)
goto err_pml5;