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Date: Thu, 8 Apr 2021 15:35:05 +0800
From: Keqian Zhu <zhukeqian1@...wei.com>
To: Ben Gardon <bgardon@...gle.com>
CC: Sean Christopherson <seanjc@...gle.com>, <kvm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
<wanghaibin.wang@...wei.com>
Subject: Re: [RFC PATCH] KVM: x86: Support write protect huge pages lazily
Hi Ben,
Do you have any similar idea that can share with us?
Thanks
Keqian
On 2021/4/7 7:42, Sean Christopherson wrote:
> +Ben
>
> On Tue, Apr 06, 2021, Keqian Zhu wrote:
>> Hi Paolo,
>>
>> I plan to rework this patch and do full test. What do you think about this idea
>> (enable dirty logging for huge pages lazily)?
>
> Ben, don't you also have something similar (or maybe the exact opposite?) in the
> hopper? This sounds very familiar, but I can't quite connect the dots that are
> floating around my head...
>
>> PS: As dirty log of TDP MMU has been supported, I should add more code.
>>
>> On 2020/8/28 16:11, Keqian Zhu wrote:
>>> Currently during enable dirty logging, if we're with init-all-set,
>>> we just write protect huge pages and leave normal pages untouched,
>>> for that we can enable dirty logging for these pages lazily.
>>>
>>> It seems that enable dirty logging lazily for huge pages is feasible
>>> too, which not only reduces the time of start dirty logging, also
>>> greatly reduces side-effect on guest when there is high dirty rate.
>>>
>>> (These codes are not tested, for RFC purpose :-) ).
>>>
>>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>>> ---
>>> arch/x86/include/asm/kvm_host.h | 3 +-
>>> arch/x86/kvm/mmu/mmu.c | 65 ++++++++++++++++++++++++++-------
>>> arch/x86/kvm/vmx/vmx.c | 3 +-
>>> arch/x86/kvm/x86.c | 22 +++++------
>>> 4 files changed, 62 insertions(+), 31 deletions(-)
>>>
>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>> index 5303dbc5c9bc..201a068cf43d 100644
>>> --- a/arch/x86/include/asm/kvm_host.h
>>> +++ b/arch/x86/include/asm/kvm_host.h
>>> @@ -1296,8 +1296,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
>>>
>>> void kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
>>> void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>>> - struct kvm_memory_slot *memslot,
>>> - int start_level);
>>> + struct kvm_memory_slot *memslot);
>>> void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>>> const struct kvm_memory_slot *memslot);
>>> void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
>>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>>> index 43fdb0c12a5d..4b7d577de6cd 100644
>>> --- a/arch/x86/kvm/mmu/mmu.c
>>> +++ b/arch/x86/kvm/mmu/mmu.c
>>> @@ -1625,14 +1625,45 @@ static bool __rmap_set_dirty(struct kvm *kvm, struct kvm_rmap_head *rmap_head)
>>> }
>>>
>>> /**
>>> - * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages
>>> + * kvm_mmu_write_protect_largepage_masked - write protect selected largepages
>>> * @kvm: kvm instance
>>> * @slot: slot to protect
>>> * @gfn_offset: start of the BITS_PER_LONG pages we care about
>>> * @mask: indicates which pages we should protect
>>> *
>>> - * Used when we do not need to care about huge page mappings: e.g. during dirty
>>> - * logging we do not have any such mappings.
>>> + * @ret: true if all pages are write protected
>>> + */
>>> +static bool kvm_mmu_write_protect_largepage_masked(struct kvm *kvm,
>>> + struct kvm_memory_slot *slot,
>>> + gfn_t gfn_offset, unsigned long mask)
>>> +{
>>> + struct kvm_rmap_head *rmap_head;
>>> + bool protected, all_protected;
>>> + gfn_t start_gfn = slot->base_gfn + gfn_offset;
>>> + int i;
>>> +
>>> + all_protected = true;
>>> + while (mask) {
>>> + protected = false;
>>> + for (i = PG_LEVEL_2M; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
>>> + rmap_head = __gfn_to_rmap(start_gfn + __ffs(mask), i, slot);
>>> + protectd |= __rmap_write_protect(kvm, rmap_head, false);
>>> + }
>>> +
>>> + all_protected &= protectd;
>>> + /* clear the first set bit */
>>> + mask &= mask - 1;
>>> + }
>>> +
>>> + return all_protected;
>>> +}
>>> +
>>> +/**
>>> + * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages
>>> + * @kvm: kvm instance
>>> + * @slot: slot to protect
>>> + * @gfn_offset: start of the BITS_PER_LONG pages we care about
>>> + * @mask: indicates which pages we should protect
>>> */
>>> static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
>>> struct kvm_memory_slot *slot,
>>> @@ -1679,18 +1710,25 @@ EXPORT_SYMBOL_GPL(kvm_mmu_clear_dirty_pt_masked);
>>>
>>> /**
>>> * kvm_arch_mmu_enable_log_dirty_pt_masked - enable dirty logging for selected
>>> - * PT level pages.
>>> - *
>>> - * It calls kvm_mmu_write_protect_pt_masked to write protect selected pages to
>>> - * enable dirty logging for them.
>>> - *
>>> - * Used when we do not need to care about huge page mappings: e.g. during dirty
>>> - * logging we do not have any such mappings.
>>> + * dirty pages.
>>> */
>>> void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
>>> struct kvm_memory_slot *slot,
>>> gfn_t gfn_offset, unsigned long mask)
>>> {
>>> + /*
>>> + * If we're with initial-all-set, huge pages are NOT
>>> + * write protected when we start dirty log, so we must
>>> + * write protect them here.
>>> + */
>>> + if (kvm_dirty_log_manual_protect_and_init_set(kvm)) {
>>> + if (kvm_mmu_write_protect_largepage_masked(kvm, slot,
>>> + gfn_offset, mask))
>>> + return;
>>> + }
>>> +
>>> + /* Then we can handle the 4K level pages */
>>> +
>>> if (kvm_x86_ops.enable_log_dirty_pt_masked)
>>> kvm_x86_ops.enable_log_dirty_pt_masked(kvm, slot, gfn_offset,
>>> mask);
>>> @@ -5906,14 +5944,13 @@ static bool slot_rmap_write_protect(struct kvm *kvm,
>>> }
>>>
>>> void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>>> - struct kvm_memory_slot *memslot,
>>> - int start_level)
>>> + struct kvm_memory_slot *memslot)
>>> {
>>> bool flush;
>>>
>>> spin_lock(&kvm->mmu_lock);
>>> - flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
>>> - start_level, KVM_MAX_HUGEPAGE_LEVEL, false);
>>> + flush = slot_handle_all_level(kvm, memslot, slot_rmap_write_protect,
>>> + false);
>>> spin_unlock(&kvm->mmu_lock);
>>>
>>> /*
>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>>> index 819c185adf09..ba871c52ef8b 100644
>>> --- a/arch/x86/kvm/vmx/vmx.c
>>> +++ b/arch/x86/kvm/vmx/vmx.c
>>> @@ -7538,8 +7538,7 @@ static void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
>>> static void vmx_slot_enable_log_dirty(struct kvm *kvm,
>>> struct kvm_memory_slot *slot)
>>> {
>>> - if (!kvm_dirty_log_manual_protect_and_init_set(kvm))
>>> - kvm_mmu_slot_leaf_clear_dirty(kvm, slot);
>>> + kvm_mmu_slot_leaf_clear_dirty(kvm, slot);
>>> kvm_mmu_slot_largepage_remove_write_access(kvm, slot);
>>> }
>>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index d39d6cf1d473..c31c32f1424b 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -10225,22 +10225,18 @@ static void kvm_mmu_slot_apply_flags(struct kvm *kvm,
>>> * is enabled the D-bit or the W-bit will be cleared.
>>> */
>>> if (new->flags & KVM_MEM_LOG_DIRTY_PAGES) {
>>> + /*
>>> + * If we're with initial-all-set, we don't need
>>> + * to write protect any page because they're
>>> + * reported as dirty already.
>>> + */
>>> + if (kvm_dirty_log_manual_protect_and_init_set(kvm))
>>> + return;
>>> +
>>> if (kvm_x86_ops.slot_enable_log_dirty) {
>>> kvm_x86_ops.slot_enable_log_dirty(kvm, new);
>>> } else {
>>> - int level =
>>> - kvm_dirty_log_manual_protect_and_init_set(kvm) ?
>>> - PG_LEVEL_2M : PG_LEVEL_4K;
>>> -
>>> - /*
>>> - * If we're with initial-all-set, we don't need
>>> - * to write protect any small page because
>>> - * they're reported as dirty already. However
>>> - * we still need to write-protect huge pages
>>> - * so that the page split can happen lazily on
>>> - * the first write to the huge page.
>>> - */
>>> - kvm_mmu_slot_remove_write_access(kvm, new, level);
>>> + kvm_mmu_slot_remove_write_access(kvm, new);
>>> }
>>> } else {
>>> if (kvm_x86_ops.slot_disable_log_dirty)
>>>
> .
>
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