On Wed, Jan 23, 2013 at 06:04:17PM +0800, Xiao Guangrong wrote:
> Do not drop large spte until it can be insteaded by small pages so that
> the guest can happliy read memory through it
>
> The idea is from Avi:
> | As I mentioned before, write-protecting a large spte is a good idea,
> | since it moves some work from protect-time to fault-time, so it reduces
> | jitter. This removes the need for the return value.
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu.c | 21 ++++++---------------
> 1 files changed, 6 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 9f628f7..0f90269 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1105,7 +1105,7 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
>
> /*
> * Write-protect on the specified @sptep, @pt_protect indicates whether
> - * spte writ-protection is caused by protecting shadow page table.
> + * spte write-protection is caused by protecting shadow page table.
> * @flush indicates whether tlb need be flushed.
> *
> * Note: write protection is difference between drity logging and spte
> @@ -1114,31 +1114,23 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
> * its dirty bitmap is properly set.
> * - for spte protection, the spte can be writable only after unsync-ing
> * shadow page.
> - *
> - * Return true if the spte is dropped.
> */
> -static bool
> +static void
> spte_write_protect(struct kvm *kvm, u64 *sptep, bool *flush, bool pt_protect)
Since return value is not longer used make the function return true if flush is needed
instead of returning it via pointer to a variable.
> {
> u64 spte = *sptep;
>
> if (!is_writable_pte(spte) &&
> !(pt_protect && spte_is_locklessly_modifiable(spte)))
> - return false;
> + return;
>
> rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
>
> - if (__drop_large_spte(kvm, sptep)) {
> - *flush |= true;
> - return true;
> - }
> -
> if (pt_protect)
> spte &= ~SPTE_MMU_WRITEABLE;
> spte = spte & ~PT_WRITABLE_MASK;
>
> *flush |= mmu_spte_update(sptep, spte);
> - return false;
> }
>
> static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
> @@ -1150,11 +1142,8 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
>
> for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
> BUG_ON(!(*sptep & PT_PRESENT_MASK));
> - if (spte_write_protect(kvm, sptep, &flush, pt_protect)) {
> - sptep = rmap_get_first(*rmapp, &iter);
> - continue;
> - }
>
> + spte_write_protect(kvm, sptep, &flush, pt_protect);
> sptep = rmap_get_next(&iter);
> }
>
> @@ -2611,6 +2600,8 @@ 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;
>
> --
> 1.7.7.6
--
Gleb.
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