Re: [PATCH v2 04/20] kvm: x86/mmu: Allocate and free TDP MMU roots

[Yu Zhang]

On Wed, Oct 14, 2020 at 11:26:44AM -0700, Ben Gardon wrote:
> The TDP MMU must be able to allocate paging structure root pages and track
> the usage of those pages. Implement a similar, but separate system for root
> page allocation to that of the x86 shadow paging implementation. When
> future patches add synchronization model changes to allow for parallel
> page faults, these pages will need to be handled differently from the
> x86 shadow paging based MMU's root pages.
> 
> Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
> machine. This series introduced no new failures.
> 
> This series can be viewed in Gerrit at:
> 	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538
> 
> Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |   1 +
>  arch/x86/kvm/mmu/mmu.c          |  29 +++++---
>  arch/x86/kvm/mmu/mmu_internal.h |  24 +++++++
>  arch/x86/kvm/mmu/tdp_mmu.c      | 114 ++++++++++++++++++++++++++++++++
>  arch/x86/kvm/mmu/tdp_mmu.h      |   5 ++
>  5 files changed, 162 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 6b6dbc20ce23a..e0ec1dd271a32 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -989,6 +989,7 @@ struct kvm_arch {
>  	 * operations.
>  	 */
>  	bool tdp_mmu_enabled;
> +	struct list_head tdp_mmu_roots;
>  };
>  
>  struct kvm_vm_stat {
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index f53d29e09367c..a3340ed59ad1d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -144,11 +144,6 @@ module_param(dbg, bool, 0644);
>  #define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | shadow_user_mask \
>  			| shadow_x_mask | shadow_nx_mask | shadow_me_mask)
>  
> -#define ACC_EXEC_MASK    1
> -#define ACC_WRITE_MASK   PT_WRITABLE_MASK
> -#define ACC_USER_MASK    PT_USER_MASK
> -#define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
> -
>  /* The mask for the R/X bits in EPT PTEs */
>  #define PT64_EPT_READABLE_MASK			0x1ull
>  #define PT64_EPT_EXECUTABLE_MASK		0x4ull
> @@ -209,7 +204,7 @@ struct kvm_shadow_walk_iterator {
>  	     __shadow_walk_next(&(_walker), spte))
>  
>  static struct kmem_cache *pte_list_desc_cache;
> -static struct kmem_cache *mmu_page_header_cache;
> +struct kmem_cache *mmu_page_header_cache;
>  static struct percpu_counter kvm_total_used_mmu_pages;
>  
>  static u64 __read_mostly shadow_nx_mask;
> @@ -3588,9 +3583,13 @@ static void mmu_free_root_page(struct kvm *kvm, hpa_t *root_hpa,
>  		return;
>  
>  	sp = to_shadow_page(*root_hpa & PT64_BASE_ADDR_MASK);
> -	--sp->root_count;
> -	if (!sp->root_count && sp->role.invalid)
> -		kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
> +
> +	if (kvm_mmu_put_root(sp)) {
> +		if (sp->tdp_mmu_page)
> +			kvm_tdp_mmu_free_root(kvm, sp);
> +		else if (sp->role.invalid)
> +			kvm_mmu_prepare_zap_page(kvm, sp, invalid_list);
> +	}
>  
>  	*root_hpa = INVALID_PAGE;
>  }
> @@ -3680,8 +3679,16 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
>  	hpa_t root;
>  	unsigned i;
>  
> -	if (shadow_root_level >= PT64_ROOT_4LEVEL) {
> -		root = mmu_alloc_root(vcpu, 0, 0, shadow_root_level, true);
> +	if (vcpu->kvm->arch.tdp_mmu_enabled) {
> +		root = kvm_tdp_mmu_get_vcpu_root_hpa(vcpu);
> +
> +		if (!VALID_PAGE(root))
> +			return -ENOSPC;
> +		vcpu->arch.mmu->root_hpa = root;
> +	} else if (shadow_root_level >= PT64_ROOT_4LEVEL) {
> +		root = mmu_alloc_root(vcpu, 0, 0, shadow_root_level,
> +				      true);
> +
>  		if (!VALID_PAGE(root))
>  			return -ENOSPC;
>  		vcpu->arch.mmu->root_hpa = root;
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 74ccbf001a42e..6cedf578c9a8d 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -43,8 +43,12 @@ struct kvm_mmu_page {
>  
>  	/* Number of writes since the last time traversal visited this page.  */
>  	atomic_t write_flooding_count;
> +
> +	bool tdp_mmu_page;
>  };
>  
> +extern struct kmem_cache *mmu_page_header_cache;
> +
>  static inline struct kvm_mmu_page *to_shadow_page(hpa_t shadow_page)
>  {
>  	struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
> @@ -96,6 +100,11 @@ bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
>  	(PT64_BASE_ADDR_MASK & ((1ULL << (PAGE_SHIFT + (((level) - 1) \
>  						* PT64_LEVEL_BITS))) - 1))
>  
> +#define ACC_EXEC_MASK    1
> +#define ACC_WRITE_MASK   PT_WRITABLE_MASK
> +#define ACC_USER_MASK    PT_USER_MASK
> +#define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
> +
>  /* Functions for interpreting SPTEs */
>  static inline bool is_mmio_spte(u64 spte)
>  {
> @@ -126,4 +135,19 @@ static inline kvm_pfn_t spte_to_pfn(u64 pte)
>  	return (pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
>  }
>  
> +static inline void kvm_mmu_get_root(struct kvm_mmu_page *sp)
> +{
> +	BUG_ON(!sp->root_count);
> +
> +	++sp->root_count;
> +}
> +
> +static inline bool kvm_mmu_put_root(struct kvm_mmu_page *sp)
> +{
> +	--sp->root_count;
> +
> +	return !sp->root_count;
> +}
> +
> +
>  #endif /* __KVM_X86_MMU_INTERNAL_H */
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index b3809835e90b1..09a84a6e157b6 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1,5 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +#include "mmu.h"
> +#include "mmu_internal.h"
>  #include "tdp_mmu.h"
>  
>  static bool __read_mostly tdp_mmu_enabled = false;
> @@ -29,10 +31,122 @@ void kvm_mmu_init_tdp_mmu(struct kvm *kvm)
>  
>  	/* This should not be changed for the lifetime of the VM. */
>  	kvm->arch.tdp_mmu_enabled = true;
> +
> +	INIT_LIST_HEAD(&kvm->arch.tdp_mmu_roots);
>  }
>  
>  void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
>  {
>  	if (!kvm->arch.tdp_mmu_enabled)
>  		return;
> +
> +	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));
> +}
> +
> +#define for_each_tdp_mmu_root(_kvm, _root)			    \
> +	list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)
> +
> +bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
> +{
> +	struct kvm_mmu_page *sp;
> +
> +	sp = to_shadow_page(hpa);
> +
> +	return sp->tdp_mmu_page && sp->root_count;
> +}
> +
> +void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
> +{
> +	lockdep_assert_held(&kvm->mmu_lock);
> +
> +	WARN_ON(root->root_count);
> +	WARN_ON(!root->tdp_mmu_page);
> +
> +	list_del(&root->link);
> +
> +	free_page((unsigned long)root->spt);
> +	kmem_cache_free(mmu_page_header_cache, root);
> +}
> +
> +static void put_tdp_mmu_root(struct kvm *kvm, struct kvm_mmu_page *root)
> +{
> +	if (kvm_mmu_put_root(root))
> +		kvm_tdp_mmu_free_root(kvm, root);
> +}
> +
> +static void get_tdp_mmu_root(struct kvm *kvm, struct kvm_mmu_page *root)
> +{
> +	lockdep_assert_held(&kvm->mmu_lock);
> +
> +	kvm_mmu_get_root(root);
> +}
> +
> +static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
> +						   int level)
> +{
> +	union kvm_mmu_page_role role;
> +
> +	role = vcpu->arch.mmu->mmu_role.base;
> +	role.level = vcpu->arch.mmu->shadow_root_level;

role.level = level;
The role will be calculated for non root pages later.

> +	role.direct = true;
> +	role.gpte_is_8_bytes = true;
> +	role.access = ACC_ALL;
> +
> +	return role;
> +}
> +
> +static struct kvm_mmu_page *alloc_tdp_mmu_page(struct kvm_vcpu *vcpu, gfn_t gfn,
> +					       int level)
> +{
> +	struct kvm_mmu_page *sp;
> +
> +	sp = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_page_header_cache);
> +	sp->spt = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache);
> +	set_page_private(virt_to_page(sp->spt), (unsigned long)sp);
> +
> +	sp->role.word = page_role_for_level(vcpu, level).word;
> +	sp->gfn = gfn;
> +	sp->tdp_mmu_page = true;
> +
> +	return sp;
> +}
> +
> +static struct kvm_mmu_page *get_tdp_mmu_vcpu_root(struct kvm_vcpu *vcpu)
> +{
> +	union kvm_mmu_page_role role;
> +	struct kvm *kvm = vcpu->kvm;
> +	struct kvm_mmu_page *root;
> +
> +	role = page_role_for_level(vcpu, vcpu->arch.mmu->shadow_root_level);
> +
> +	spin_lock(&kvm->mmu_lock);
> +
> +	/* Check for an existing root before allocating a new one. */
> +	for_each_tdp_mmu_root(kvm, root) {
> +		if (root->role.word == role.word) {
> +			get_tdp_mmu_root(kvm, root);
> +			spin_unlock(&kvm->mmu_lock);
> +			return root;
> +		}
> +	}
> +
> +	root = alloc_tdp_mmu_page(vcpu, 0, vcpu->arch.mmu->shadow_root_level);
> +	root->root_count = 1;
> +
> +	list_add(&root->link, &kvm->arch.tdp_mmu_roots);
> +
> +	spin_unlock(&kvm->mmu_lock);
> +
> +	return root;
> +}
> +
> +hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_mmu_page *root;
> +
> +	root = get_tdp_mmu_vcpu_root(vcpu);
> +	if (!root)
> +		return INVALID_PAGE;
> +
> +	return __pa(root->spt);
>  }
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index cd4a562a70e9a..ac0ef91294420 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -7,4 +7,9 @@
>  
>  void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
>  void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
> +
> +bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
> +hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
> +void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root);
> +
>  #endif /* __KVM_X86_MMU_TDP_MMU_H */
> -- 
> 2.28.0.1011.ga647a8990f-goog
> 

Thanks
Yu