Re: [PATCH] KVM: nVMX: fix shadow on EPT

[Paolo Bonzini <pbonzini@redhat.com>]

Il 09/10/2013 18:13, Gleb Natapov ha scritto:
> 72f857950f6f19 broke shadow on EPT. This patch reverts it and fixes PAE
> on nEPT (which reverted commit fixed) in other way.
> 
> Shadow on EPT is now broken because while L1 builds shadow page table
> for L2 (which is PAE while L2 is in real mode) it never loads L2's
> GUEST_PDPTR[0-3].  They do not need to be loaded because without nested
> virtualization HW does this during guest entry if EPT is disabled,
> but in our case L0 emulates L2's vmentry while EPT is enables, so we
> cannot rely on vmcs12->guest_pdptr[0-3] to contain up-to-date values
> and need to re-read PDPTEs from L2 memory. This is what kvm_set_cr3()
> is doing, but by clearing cache bits during L2 vmentry we drop values
> that kvm_set_cr3() read from memory.
> 
> So why the same code does not work for PAE on nEPT? kvm_set_cr3()
> reads pdptes into vcpu->arch.walk_mmu->pdptrs[]. walk_mmu points to
> vcpu->arch.nested_mmu while nested guest is running, but ept_load_pdptrs()
> uses vcpu->arch.mmu which contain incorrect values. Fix that by using
> walk_mmu in ept_(load|save)_pdptrs.
> 
> Signed-off-by: Gleb Natapov <gleb@redhat.com>

The new fix also looks much more obvious.

Applied to queue, thanks.

Paolo