Date:   Wed, 7 Dec 2022 16:13:14 +0800
From:   Yuan Yao <yuan.yao@...ux.intel.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 6/9] KVM: Unmap existing mappings when change the
 memory attributes

On Fri, Dec 02, 2022 at 02:13:44PM +0800, Chao Peng wrote:
> Unmap the existing guest mappings when memory attribute is changed
> between shared and private. This is needed because shared pages and
> private pages are from different backends, unmapping existing ones
> gives a chance for page fault handler to re-populate the mappings
> according to the new attribute.
>
> Only architecture has private memory support needs this and the
> supported architecture is expected to rewrite the weak
> kvm_arch_has_private_mem().
>
> Also, during memory attribute changing and the unmapping time frame,
> page fault handler may happen in the same memory range and can cause
> incorrect page state, invoke kvm_mmu_invalidate_* helpers to let the
> page fault handler retry during this time frame.
>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> ---
>  include/linux/kvm_host.h |   7 +-
>  virt/kvm/kvm_main.c      | 168 ++++++++++++++++++++++++++-------------
>  2 files changed, 116 insertions(+), 59 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3d69484d2704..3331c0c92838 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -255,7 +255,6 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
>  #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  struct kvm_gfn_range {
>  	struct kvm_memory_slot *slot;
>  	gfn_t start;
> @@ -264,6 +263,8 @@ struct kvm_gfn_range {
>  	bool may_block;
>  };
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> +
> +#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
>  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
>  bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range);
> @@ -785,11 +786,12 @@ struct kvm {
>
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  	struct mmu_notifier mmu_notifier;
> +#endif
>  	unsigned long mmu_invalidate_seq;
>  	long mmu_invalidate_in_progress;
>  	gfn_t mmu_invalidate_range_start;
>  	gfn_t mmu_invalidate_range_end;
> -#endif
> +
>  	struct list_head devices;
>  	u64 manual_dirty_log_protect;
>  	struct dentry *debugfs_dentry;
> @@ -1480,6 +1482,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
>  int kvm_arch_post_init_vm(struct kvm *kvm);
>  void kvm_arch_pre_destroy_vm(struct kvm *kvm);
>  int kvm_arch_create_vm_debugfs(struct kvm *kvm);
> +bool kvm_arch_has_private_mem(struct kvm *kvm);
>
>  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
>  /*
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ad55dfbc75d7..4e1e1e113bf0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -520,6 +520,62 @@ void kvm_destroy_vcpus(struct kvm *kvm)
>  }
>  EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>
> +void kvm_mmu_invalidate_begin(struct kvm *kvm)
> +{
> +	/*
> +	 * The count increase must become visible at unlock time as no
> +	 * spte can be established without taking the mmu_lock and
> +	 * count is also read inside the mmu_lock critical section.
> +	 */
> +	kvm->mmu_invalidate_in_progress++;
> +
> +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +		kvm->mmu_invalidate_range_start = INVALID_GPA;
> +		kvm->mmu_invalidate_range_end = INVALID_GPA;
> +	}
> +}
> +
> +void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> +
> +	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> +		kvm->mmu_invalidate_range_start = start;
> +		kvm->mmu_invalidate_range_end = end;
> +	} else {
> +		/*
> +		 * Fully tracking multiple concurrent ranges has diminishing
> +		 * returns. Keep things simple and just find the minimal range
> +		 * which includes the current and new ranges. As there won't be
> +		 * enough information to subtract a range after its invalidate
> +		 * completes, any ranges invalidated concurrently will
> +		 * accumulate and persist until all outstanding invalidates
> +		 * complete.
> +		 */
> +		kvm->mmu_invalidate_range_start =
> +			min(kvm->mmu_invalidate_range_start, start);
> +		kvm->mmu_invalidate_range_end =
> +			max(kvm->mmu_invalidate_range_end, end);
> +	}
> +}
> +
> +void kvm_mmu_invalidate_end(struct kvm *kvm)
> +{
> +	/*
> +	 * This sequence increase will notify the kvm page fault that
> +	 * the page that is going to be mapped in the spte could have
> +	 * been freed.
> +	 */
> +	kvm->mmu_invalidate_seq++;
> +	smp_wmb();
> +	/*
> +	 * The above sequence increase must be visible before the
> +	 * below count decrease, which is ensured by the smp_wmb above
> +	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> +	 */
> +	kvm->mmu_invalidate_in_progress--;
> +}
> +
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
>  {
> @@ -714,45 +770,6 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
>  	kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
>  }
>
> -void kvm_mmu_invalidate_begin(struct kvm *kvm)
> -{
> -	/*
> -	 * The count increase must become visible at unlock time as no
> -	 * spte can be established without taking the mmu_lock and
> -	 * count is also read inside the mmu_lock critical section.
> -	 */
> -	kvm->mmu_invalidate_in_progress++;
> -
> -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -		kvm->mmu_invalidate_range_start = INVALID_GPA;
> -		kvm->mmu_invalidate_range_end = INVALID_GPA;
> -	}
> -}
> -
> -void kvm_mmu_invalidate_range_add(struct kvm *kvm, gfn_t start, gfn_t end)
> -{
> -	WARN_ON_ONCE(!kvm->mmu_invalidate_in_progress);
> -
> -	if (likely(kvm->mmu_invalidate_in_progress == 1)) {
> -		kvm->mmu_invalidate_range_start = start;
> -		kvm->mmu_invalidate_range_end = end;
> -	} else {
> -		/*
> -		 * Fully tracking multiple concurrent ranges has diminishing
> -		 * returns. Keep things simple and just find the minimal range
> -		 * which includes the current and new ranges. As there won't be
> -		 * enough information to subtract a range after its invalidate
> -		 * completes, any ranges invalidated concurrently will
> -		 * accumulate and persist until all outstanding invalidates
> -		 * complete.
> -		 */
> -		kvm->mmu_invalidate_range_start =
> -			min(kvm->mmu_invalidate_range_start, start);
> -		kvm->mmu_invalidate_range_end =
> -			max(kvm->mmu_invalidate_range_end, end);
> -	}
> -}
> -
>  static bool kvm_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
>  {
>  	kvm_mmu_invalidate_range_add(kvm, range->start, range->end);
> @@ -806,23 +823,6 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  	return 0;
>  }
>
> -void kvm_mmu_invalidate_end(struct kvm *kvm)
> -{
> -	/*
> -	 * This sequence increase will notify the kvm page fault that
> -	 * the page that is going to be mapped in the spte could have
> -	 * been freed.
> -	 */
> -	kvm->mmu_invalidate_seq++;
> -	smp_wmb();
> -	/*
> -	 * The above sequence increase must be visible before the
> -	 * below count decrease, which is ensured by the smp_wmb above
> -	 * in conjunction with the smp_rmb in mmu_invalidate_retry().
> -	 */
> -	kvm->mmu_invalidate_in_progress--;
> -}
> -
>  static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
>  					const struct mmu_notifier_range *range)
>  {
> @@ -1140,6 +1140,11 @@ int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
>  	return 0;
>  }
>
> +bool __weak kvm_arch_has_private_mem(struct kvm *kvm)
> +{
> +	return false;
> +}
> +
>  static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>  {
>  	struct kvm *kvm = kvm_arch_alloc_vm();
> @@ -2349,15 +2354,47 @@ static u64 kvm_supported_mem_attributes(struct kvm *kvm)
>  	return 0;
>  }
>
> +static void kvm_unmap_mem_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	struct kvm_gfn_range gfn_range;
> +	struct kvm_memory_slot *slot;
> +	struct kvm_memslots *slots;
> +	struct kvm_memslot_iter iter;
> +	int i;
> +	int r = 0;
> +
> +	gfn_range.pte = __pte(0);
> +	gfn_range.may_block = true;
> +
> +	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> +		slots = __kvm_memslots(kvm, i);
> +
> +		kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
> +			slot = iter.slot;
> +			gfn_range.start = max(start, slot->base_gfn);
> +			gfn_range.end = min(end, slot->base_gfn + slot->npages);
> +			if (gfn_range.start >= gfn_range.end)
> +				continue;
> +			gfn_range.slot = slot;
> +
> +			r |= kvm_unmap_gfn_range(kvm, &gfn_range);
> +		}
> +	}
> +
> +	if (r)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> +
>  static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  					   struct kvm_memory_attributes *attrs)
>  {
>  	gfn_t start, end;
>  	unsigned long i;
>  	void *entry;
> +	int idx;
>  	u64 supported_attrs = kvm_supported_mem_attributes(kvm);
>
> -	/* flags is currently not used. */
> +	/* 'flags' is currently not used. */
>  	if (attrs->flags)
>  		return -EINVAL;
>  	if (attrs->attributes & ~supported_attrs)
> @@ -2372,6 +2409,13 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>
>  	entry = attrs->attributes ? xa_mk_value(attrs->attributes) : NULL;
>
> +	if (kvm_arch_has_private_mem(kvm)) {
> +		KVM_MMU_LOCK(kvm);
> +		kvm_mmu_invalidate_begin(kvm);
> +		kvm_mmu_invalidate_range_add(kvm, start, end);

Nit: this works for KVM_MEMORY_ATTRIBUTE_PRIVATE, but
the invalidation should be necessary yet for attribute change of:

KVM_MEMORY_ATTRIBUTE_READ
KVM_MEMORY_ATTRIBUTE_WRITE
KVM_MEMORY_ATTRIBUTE_EXECUTE

> +		KVM_MMU_UNLOCK(kvm);
> +	}
> +
>  	mutex_lock(&kvm->lock);
>  	for (i = start; i < end; i++)
>  		if (xa_err(xa_store(&kvm->mem_attr_array, i, entry,
> @@ -2379,6 +2423,16 @@ static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
>  			break;
>  	mutex_unlock(&kvm->lock);
>
> +	if (kvm_arch_has_private_mem(kvm)) {
> +		idx = srcu_read_lock(&kvm->srcu);
> +		KVM_MMU_LOCK(kvm);
> +		if (i > start)
> +			kvm_unmap_mem_range(kvm, start, i);
> +		kvm_mmu_invalidate_end(kvm);

Ditto.

> +		KVM_MMU_UNLOCK(kvm);
> +		srcu_read_unlock(&kvm->srcu, idx);
> +	}
> +
>  	attrs->address = i << PAGE_SHIFT;
>  	attrs->size = (end - i) << PAGE_SHIFT;
>
> --
> 2.25.1
>
>

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