Message-ID: <20221208022918.fbddl3bflsip4ivg@yy-desk-7060>
Date:   Thu, 8 Dec 2022 10:29:18 +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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        Wanpeng Li <wanpengli@...cent.com>,
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        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
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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 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' ?

> +
>  	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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