On Oct 1, 2013, at 7:05 AM, Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote:
> On Thu, Sep 05, 2013 at 06:29:08PM +0800, Xiao Guangrong wrote:
>> Now we can flush all the TLBs out of the mmu lock without TLB corruption when
>> write-proect the sptes, it is because:
>> - we have marked large sptes readonly instead of dropping them that means we
>> just change the spte from writable to readonly so that we only need to care
>> the case of changing spte from present to present (changing the spte from
>> present to nonpresent will flush all the TLBs immediately), in other words,
>> the only case we need to care is mmu_spte_update()
>>
>> - in mmu_spte_update(), we have checked
>> SPTE_HOST_WRITEABLE | PTE_MMU_WRITEABLE instead of PT_WRITABLE_MASK, that
>> means it does not depend on PT_WRITABLE_MASK anymore
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
>> ---
>> arch/x86/kvm/mmu.c | 18 ++++++++++++++----
>> arch/x86/kvm/x86.c | 9 +++++++--
>> 2 files changed, 21 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 7488229..a983570 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -4320,15 +4320,25 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
>> if (*rmapp)
>> __rmap_write_protect(kvm, rmapp, false);
>>
>> - if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
>> - kvm_flush_remote_tlbs(kvm);
>> + if (need_resched() || spin_needbreak(&kvm->mmu_lock))
>> cond_resched_lock(&kvm->mmu_lock);
>> - }
>> }
>> }
>>
>> - kvm_flush_remote_tlbs(kvm);
>> spin_unlock(&kvm->mmu_lock);
>> +
>> + /*
>> + * We can flush all the TLBs out of the mmu lock without TLB
>> + * corruption since we just change the spte from writable to
>> + * readonly so that we only need to care the case of changing
>> + * spte from present to present (changing the spte from present
>> + * to nonpresent will flush all the TLBs immediately), in other
>> + * words, the only case we care is mmu_spte_update() where we
>> + * haved checked SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE
>> + * instead of PT_WRITABLE_MASK, that means it does not depend
>> + * on PT_WRITABLE_MASK anymore.
>> + */
>> + kvm_flush_remote_tlbs(kvm);
>> }
>
> What about need_remote_flush?
It is safe because before calling need_remote_flush mmu_pte_write_new_pte is called to
update the spte which will finally call set_spte() where the tlb flush has been properly checked.
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