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

From: Paolo Bonzini
Date: Wed Oct 21 2020 - 14:01:27 EST

On 21/10/20 19:54, Ben Gardon wrote:
> On Wed, Oct 21, 2020 at 8:09 AM Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>
>> 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.
>
> Thank you for catching that Yu, that was definitely an error!
> I'm guessing this never showed up in my testing because I don't think
> the TDP MMU actually uses role.level for anything other than root
> pages.

I'll fix it up, thanks to both!

Paolo