Re: [PATCH 09/13] KVM: MMU: get expected spte out of mmu-lock

Avi Kivity
2012-04-01T15:53:18Z

On 03/29/2012 11:25 AM, Xiao Guangrong wrote:
> It depends on PTE_LIST_WRITE_PROTECT bit in rmap which let us quickly know
> whether the page is writable out of mmu-lock
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/mmu.c | 17 +++++++++++++----
> arch/x86/kvm/paging_tmpl.h | 2 +-
> 2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 3887a07..c029185 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1148,6 +1148,12 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
>
> *rmapp |= PTE_LIST_WRITE_PROTECT;
>
> + /*
> + * Setting PTE_LIST_WRITE_PROTECT bit before doing page
> + * write-protect.
> + */
> + smp_mb();
> +

wmb only needed.

Would it be better to store this bit in all the sptes instead? We're
touching them in any case. More work to clear them, but
un-write-protecting a page is beneficial anyway as it can save a fault.

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