Re: KVM: MMU: only write protect mappings at pagetable level

[Avi Kivity <avi@redhat.com>]

On 12/22/2010 01:01 PM, Marcelo Tosatti wrote:
> If a pagetable contains a writeable large spte, all of its sptes will be

non-writeable

> write protected, including non-leaf ones, leading to endless pagefaults.
>
> Do not write protect pages above PT_PAGE_TABLE_LEVEL, as the spte fault
> paths assume non-leaf sptes are writable.
>
> Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index c3853d5..c716ff8 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -3442,6 +3442,9 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
>   		if (!test_bit(slot, sp->slot_bitmap))
>   			continue;
>
> +		if (sp->role.level != PT_PAGE_TABLE_LEVEL)
> +			continue;
> +
>   		pt = sp->spt;
>   		for (i = 0; i<  PT64_ENT_PER_PAGE; ++i)
>   			/* avoid RMW */

But what about large leaf sptes?  Don't we want to write protect, or 
perhaps drop them?

I think write-protecting leaf sptes and ignoring nonleaf sptes should work.

-- 
error compiling committee.c: too many arguments to function