Re: KVM: MMU: drop read-only large sptes when creating lower level sptes

[Paolo Bonzini <pbonzini@redhat.com>]

Il 24/02/2014 17:59, Marcelo Tosatti ha scritto:
>
> Read-only large sptes can be created due to read-only faults as
> follows:
>
> - QEMU pagetable entry that maps guest memory is read-only
> due to COW.
> - Guest read faults such memory, COW is not broken, because
> it is a read-only fault.
> - Enable dirty logging, large spte not nuked because it is read-only.
> - Write-fault on such memory causes guest to loop endlessly
> (which must go down to level 1 because dirty logging is enabled).
>
> Fix by dropping large spte when necessary.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index e50425d..9b53135 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -2672,6 +2672,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
>  			break;
>  		}
>
> +		drop_large_spte(vcpu, iterator.sptep);
>  		if (!is_shadow_present_pte(*iterator.sptep)) {
>  			u64 base_addr = iterator.addr;
>
>
>

Queued for kvm/master, will push as soon as I test it.

Thanks,

Paolo