[PATCH 5.1 104/121] KVM: x86/mmu: Allocate PAE root array when using SVMs 32-bit NPT

[Greg Kroah-Hartman]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

commit b6b80c78af838bef17501416d5d383fedab0010a upstream.

SVM's Nested Page Tables (NPT) reuses x86 paging for the host-controlled
page walk.  For 32-bit KVM, this means PAE paging is used even when TDP
is enabled, i.e. the PAE root array needs to be allocated.

Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Jiri Palecek <jpalecek@xxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kvm/mmu.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5591,14 +5591,18 @@ static int alloc_mmu_pages(struct kvm_vc
 	struct page *page;
 	int i;
 
-	if (tdp_enabled)
-		return 0;
-
 	/*
-	 * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
-	 * Therefore we need to allocate shadow page tables in the first
-	 * 4GB of memory, which happens to fit the DMA32 zone.
+	 * When using PAE paging, the four PDPTEs are treated as 'root' pages,
+	 * while the PDP table is a per-vCPU construct that's allocated at MMU
+	 * creation.  When emulating 32-bit mode, cr3 is only 32 bits even on
+	 * x86_64.  Therefore we need to allocate the PDP table in the first
+	 * 4GB of memory, which happens to fit the DMA32 zone.  Except for
+	 * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
+	 * skip allocating the PDP table.
 	 */
+	if (tdp_enabled && kvm_x86_ops->get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
+		return 0;
+
 	page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_DMA32);
 	if (!page)
 		return -ENOMEM;