On Fri, Apr 20, 2012 at 04:17:47PM +0800, Xiao Guangrong wrote:
> Introduce a common function to abstract spte write-protect to
> cleanup the code
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 60 ++++++++++++++++++++++++++++++---------------------
> 1 files changed, 35 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 4a3cc18..e70ff38 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1041,6 +1041,34 @@ static void drop_spte(struct kvm *kvm, u64 *sptep)
> rmap_remove(kvm, sptep);
> }
>
> +/* Return true if the spte is dropped. */
> +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool large,
> + bool *flush)
> +{
> + u64 spte = *sptep;
> +
> + if (!is_writable_pte(spte))
> + return false;
> +
> + *flush |= true;
> +
> + if (large) {
> + pgprintk("rmap_write_protect(large): spte %p %llx\n",
> + spte, *spte);
> + BUG_ON(!is_large_pte(spte));
> +
> + drop_spte(kvm, sptep);
> + --kvm->stat.lpages;
> + return true;
> + }
> +
> + rmap_printk("rmap_write_protect: spte %p %llx\n", spte, *spte);
> + spte = spte & ~PT_WRITABLE_MASK;
> + mmu_spte_update(sptep, spte);
> +
> + return false;
> +}
> +
> static bool
> __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level)
> {
> @@ -1050,24 +1078,13 @@ __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level)
>
> for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
> BUG_ON(!(*sptep & PT_PRESENT_MASK));
> - rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
> -
> - if (!is_writable_pte(*sptep)) {
> - sptep = rmap_get_next(&iter);
> - continue;
> - }
> -
> - if (level == PT_PAGE_TABLE_LEVEL) {
> - mmu_spte_update(sptep, *sptep & ~PT_WRITABLE_MASK);
> - sptep = rmap_get_next(&iter);
> - } else {
> - BUG_ON(!is_large_pte(*sptep));
> - drop_spte(kvm, sptep);
> - --kvm->stat.lpages;
It is preferable to remove all large sptes including read-only ones, the
current behaviour, then to verify that no read->write transition can
occur in fault paths (fault paths which are increasing in number).
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