Message-ID: <20221209054517.okw2epqx5s3yjnfp@yy-desk-7060>
Date:   Fri, 9 Dec 2022 13:45:17 +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,
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        Jonathan Corbet <corbet@....net>,
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        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
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        Yu Zhang <yu.c.zhang@...ux.intel.com>,
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        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

On Thu, Dec 08, 2022 at 07:23:46PM +0800, Chao Peng wrote:
> On Thu, Dec 08, 2022 at 10:29:18AM +0800, Yuan Yao wrote:
> > On Fri, Dec 02, 2022 at 02:13:46PM +0800, Chao Peng wrote:
> > > A KVM_MEM_PRIVATE memslot can include both fd-based private memory and
> > > hva-based shared memory. Architecture code (like TDX code) can tell
> > > whether the on-going fault is private or not. This patch adds a
> > > 'is_private' field to kvm_page_fault to indicate this and architecture
> > > code is expected to set it.
> > >
> > > To handle page fault for such memslot, the handling logic is different
> > > depending on whether the fault is private or shared. KVM checks if
> > > 'is_private' matches the host's view of the page (maintained in
> > > mem_attr_array).
> > >   - For a successful match, private pfn is obtained with
> > >     restrictedmem_get_page() and shared pfn is obtained with existing
> > >     get_user_pages().
> > >   - For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
> > >     userspace. Userspace then can convert memory between private/shared
> > >     in host's view and retry the fault.
> > >
> > > Co-developed-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> > > Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> > > Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> > > ---
> > >  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++++++++++++++--
> > >  arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
> > >  arch/x86/kvm/mmu/mmutrace.h     |  1 +
> > >  arch/x86/kvm/mmu/tdp_mmu.c      |  2 +-
> > >  include/linux/kvm_host.h        | 30 ++++++++++++++++
> > >  5 files changed, 105 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 2190fd8c95c0..b1953ebc012e 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -3058,7 +3058,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
> > >
> > >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > > -			      int max_level)
> > > +			      int max_level, bool is_private)
> > >  {
> > >  	struct kvm_lpage_info *linfo;
> > >  	int host_level;
> > > @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			break;
> > >  	}
> > >
> > > +	if (is_private)
> > > +		return max_level;
> >
> > lpage mixed information already saved, so is that possible
> > to query info->disallow_lpage without care 'is_private' ?
>
> Actually we already queried info->disallow_lpage just before this
> sentence. The check is needed because later in the function we call
> host_pfn_mapping_level() which is shared memory specific.

You're right. We can't get mapping level info for private page from
host_pfn_mapping_level().

>
> Thanks,
> Chao
> >
> > > +
> > >  	if (max_level == PG_LEVEL_4K)
> > >  		return PG_LEVEL_4K;
> > >
> > > @@ -3098,7 +3101,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> > >  	 * level, which will be used to do precise, accurate accounting.
> > >  	 */
> > >  	fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> > > -						     fault->gfn, fault->max_level);
> > > +						     fault->gfn, fault->max_level,
> > > +						     fault->is_private);
> > >  	if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> > >  		return;
> > >
> > > @@ -4178,6 +4182,49 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> > >  	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
> > >  }
> > >
> > > +static inline u8 order_to_level(int order)
> > > +{
> > > +	BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> > > +
> > > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> > > +		return PG_LEVEL_1G;
> > > +
> > > +	if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> > > +		return PG_LEVEL_2M;
> > > +
> > > +	return PG_LEVEL_4K;
> > > +}
> > > +
> > > +static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> > > +				    struct kvm_page_fault *fault)
> > > +{
> > > +	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> > > +	if (fault->is_private)
> > > +		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> > > +	else
> > > +		vcpu->run->memory.flags = 0;
> > > +	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> > > +	vcpu->run->memory.size = PAGE_SIZE;
> > > +	return RET_PF_USER;
> > > +}
> > > +
> > > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > > +				   struct kvm_page_fault *fault)
> > > +{
> > > +	int order;
> > > +	struct kvm_memory_slot *slot = fault->slot;
> > > +
> > > +	if (!kvm_slot_can_be_private(slot))
> > > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > > +
> > > +	if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> > > +		return RET_PF_RETRY;
> > > +
> > > +	fault->max_level = min(order_to_level(order), fault->max_level);
> > > +	fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> > > +	return RET_PF_CONTINUE;
> > > +}
> > > +
> > >  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > >  {
> > >  	struct kvm_memory_slot *slot = fault->slot;
> > > @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > >  			return RET_PF_EMULATE;
> > >  	}
> > >
> > > +	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> > > +		return kvm_do_memory_fault_exit(vcpu, fault);
> > > +
> > > +	if (fault->is_private)
> > > +		return kvm_faultin_pfn_private(vcpu, fault);
> > > +
> > >  	async = false;
> > >  	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> > >  					  fault->write, &fault->map_writable,
> > > @@ -5599,6 +5652,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
> > >  			return -EIO;
> > >  	}
> > >
> > > +	if (r == RET_PF_USER)
> > > +		return 0;
> > > +
> > >  	if (r < 0)
> > >  		return r;
> > >  	if (r != RET_PF_EMULATE)
> > > @@ -6452,7 +6508,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> > >  		 */
> > >  		if (sp->role.direct &&
> > >  		    sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> > > -							       PG_LEVEL_NUM)) {
> > > +							       PG_LEVEL_NUM,
> > > +							       false)) {
> > >  			kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
> > >
> > >  			if (kvm_available_flush_tlb_with_range())
> > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > > index dbaf6755c5a7..5ccf08183b00 100644
> > > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > > @@ -189,6 +189,7 @@ struct kvm_page_fault {
> > >
> > >  	/* Derived from mmu and global state.  */
> > >  	const bool is_tdp;
> > > +	const bool is_private;
> > >  	const bool nx_huge_page_workaround_enabled;
> > >
> > >  	/*
> > > @@ -237,6 +238,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> > >   * RET_PF_RETRY: let CPU fault again on the address.
> > >   * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
> > >   * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> > > + * RET_PF_USER: need to exit to userspace to handle this fault.
> > >   * RET_PF_FIXED: The faulting entry has been fixed.
> > >   * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
> > >   *
> > > @@ -253,6 +255,7 @@ enum {
> > >  	RET_PF_RETRY,
> > >  	RET_PF_EMULATE,
> > >  	RET_PF_INVALID,
> > > +	RET_PF_USER,
> > >  	RET_PF_FIXED,
> > >  	RET_PF_SPURIOUS,
> > >  };
> > > @@ -310,7 +313,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >
> > >  int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > >  			      const struct kvm_memory_slot *slot, gfn_t gfn,
> > > -			      int max_level);
> > > +			      int max_level, bool is_private);
> > >  void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> > >  void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
> > >
> > > @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> > >  void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > >  void untrack_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > >
> > > +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > > +{
> > > +	WARN_ON_ONCE(1);
> > > +	return -EOPNOTSUPP;
> > > +}
> > > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > > +
> > >  #endif /* __KVM_X86_MMU_INTERNAL_H */
> > > diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> > > index ae86820cef69..2d7555381955 100644
> > > --- a/arch/x86/kvm/mmu/mmutrace.h
> > > +++ b/arch/x86/kvm/mmu/mmutrace.h
> > > @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
> > >  TRACE_DEFINE_ENUM(RET_PF_RETRY);
> > >  TRACE_DEFINE_ENUM(RET_PF_EMULATE);
> > >  TRACE_DEFINE_ENUM(RET_PF_INVALID);
> > > +TRACE_DEFINE_ENUM(RET_PF_USER);
> > >  TRACE_DEFINE_ENUM(RET_PF_FIXED);
> > >  TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
> > >
> > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > > index 771210ce5181..8ba1a4afc546 100644
> > > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > > @@ -1768,7 +1768,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
> > >  			continue;
> > >
> > >  		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> > > -							      iter.gfn, PG_LEVEL_NUM);
> > > +						iter.gfn, PG_LEVEL_NUM, false);
> > >  		if (max_mapping_level < iter.level)
> > >  			continue;
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 25099c94e770..153842bb33df 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > >  }
> > >  #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> > >
> > > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > > +{
> > > +	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> > > +	       KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > > +}
> > > +#else
> > > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > > +{
> > > +	return false;
> > > +}
> > > +
> > > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > > +
> > > +#ifdef CONFIG_HAVE_KVM_RESTRICTED_MEM
> > > +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> > > +					gfn_t gfn, kvm_pfn_t *pfn, int *order)
> > > +{
> > > +	int ret;
> > > +	struct page *page;
> > > +	pgoff_t index = gfn - slot->base_gfn +
> > > +			(slot->restricted_offset >> PAGE_SHIFT);
> > > +
> > > +	ret = restrictedmem_get_page(slot->restricted_file, index,
> > > +				     &page, order);
> > > +	*pfn = page_to_pfn(page);
> > > +	return ret;
> > > +}
> > > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > > +
> > >  #endif
> > > --
> > > 2.25.1
> > >
> > >

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