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Date: Wed, 21 Oct 2020 23:09:17 +0800
From: Yu Zhang <yu.c.zhang@...ux.intel.com>
To: Ben Gardon <bgardon@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
Cannon Matthews <cannonmatthews@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Peter Xu <peterx@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Peter Shier <pshier@...gle.com>,
Peter Feiner <pfeiner@...gle.com>,
Junaid Shahid <junaids@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
Yulei Zhang <yulei.kernel@...il.com>,
Wanpeng Li <kernellwp@...il.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Xiao Guangrong <xiaoguangrong.eric@...il.com>
Subject: Re: [PATCH v2 04/20] kvm: x86/mmu: Allocate and free TDP MMU roots
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@...gle.com>
> ---
> 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
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