Message-ID: <20221209054305.e3hlnfh7ptxtkoek@yy-desk-7060>
Date:   Fri, 9 Dec 2022 13:43:05 +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 Thu, Dec 08, 2022 at 07:20:43PM +0800, Chao Peng wrote:
> On Wed, Dec 07, 2022 at 04:13:14PM +0800, Yuan Yao wrote:
> > 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
>
> The unmapping is only needed for confidential usages which uses
> KVM_MEMORY_ATTRIBUTE_PRIVATE only and the other flags are defined here
> for other usages like pKVM. As Fuad commented in a different reply, pKVM
> supports in-place remapping and unmapping is unnecessary.

Ah, I see. It's fine to me, thanks.

>
> Thanks,
> Chao
> >
> > > +		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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