Re: [PATCH v2 07/20] kvm: x86/mmu: Support zapping SPTEs in the TDP MMU

[Yu Zhang]

On Wed, Oct 14, 2020 at 11:26:47AM -0700, Ben Gardon wrote:
> Add functions to zap SPTEs to the TDP MMU. These are needed to tear down
> TDP MMU roots properly and implement other MMU functions which require
> tearing down mappings. Future patches will add functions to populate the
> page tables, but as for this patch there will not be any work for these
> functions to do.
> 
> 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/kvm/mmu/mmu.c      |  15 +++++
>  arch/x86/kvm/mmu/tdp_iter.c |   5 ++
>  arch/x86/kvm/mmu/tdp_iter.h |   1 +
>  arch/x86/kvm/mmu/tdp_mmu.c  | 109 ++++++++++++++++++++++++++++++++++++
>  arch/x86/kvm/mmu/tdp_mmu.h  |   2 +
>  5 files changed, 132 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 8bf20723c6177..337ab6823e312 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5787,6 +5787,10 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm)
>  	kvm_reload_remote_mmus(kvm);
>  
>  	kvm_zap_obsolete_pages(kvm);
> +
> +	if (kvm->arch.tdp_mmu_enabled)
> +		kvm_tdp_mmu_zap_all(kvm);
> +
>  	spin_unlock(&kvm->mmu_lock);
>  }
>  
> @@ -5827,6 +5831,7 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>  	struct kvm_memslots *slots;
>  	struct kvm_memory_slot *memslot;
>  	int i;
> +	bool flush;
>  
>  	spin_lock(&kvm->mmu_lock);
>  	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> @@ -5846,6 +5851,12 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>  		}
>  	}
>  
> +	if (kvm->arch.tdp_mmu_enabled) {
> +		flush = kvm_tdp_mmu_zap_gfn_range(kvm, gfn_start, gfn_end);
> +		if (flush)
> +			kvm_flush_remote_tlbs(kvm);
> +	}
> +
>  	spin_unlock(&kvm->mmu_lock);
>  }
>  
> @@ -6012,6 +6023,10 @@ void kvm_mmu_zap_all(struct kvm *kvm)
>  	}
>  
>  	kvm_mmu_commit_zap_page(kvm, &invalid_list);
> +
> +	if (kvm->arch.tdp_mmu_enabled)
> +		kvm_tdp_mmu_zap_all(kvm);
> +
>  	spin_unlock(&kvm->mmu_lock);
>  }
>  
> diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c
> index b07e9f0c5d4aa..701eb753b701e 100644
> --- a/arch/x86/kvm/mmu/tdp_iter.c
> +++ b/arch/x86/kvm/mmu/tdp_iter.c
> @@ -174,3 +174,8 @@ void tdp_iter_refresh_walk(struct tdp_iter *iter)
>  		       iter->root_level, iter->min_level, goal_gfn);
>  }
>  
> +u64 *tdp_iter_root_pt(struct tdp_iter *iter)
> +{
> +	return iter->pt_path[iter->root_level - 1];
> +}
> +
> diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h
> index d629a53e1b73f..884ed2c70bfed 100644
> --- a/arch/x86/kvm/mmu/tdp_iter.h
> +++ b/arch/x86/kvm/mmu/tdp_iter.h
> @@ -52,5 +52,6 @@ void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
>  		    int min_level, gfn_t goal_gfn);
>  void tdp_iter_next(struct tdp_iter *iter);
>  void tdp_iter_refresh_walk(struct tdp_iter *iter);
> +u64 *tdp_iter_root_pt(struct tdp_iter *iter);
>  
>  #endif /* __KVM_X86_MMU_TDP_ITER_H */
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index f2bd3a6928ce9..9b5cd4a832f1a 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -56,8 +56,13 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
>  	return sp->tdp_mmu_page && sp->root_count;
>  }
>  
> +static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> +			  gfn_t start, gfn_t end);
> +
>  void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
>  {
> +	gfn_t max_gfn = 1ULL << (boot_cpu_data.x86_phys_bits - PAGE_SHIFT);
> +

boot_cpu_data.x86_phys_bits is the host address width. Value of the guest's
may vary. So maybe we should just traverse the memslots and zap the gfn ranges
in each of them?

>  	lockdep_assert_held(&kvm->mmu_lock);
>  
>  	WARN_ON(root->root_count);
> @@ -65,6 +70,8 @@ void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root)
>  
>  	list_del(&root->link);
>  
> +	zap_gfn_range(kvm, root, 0, max_gfn);
> +
>  	free_page((unsigned long)root->spt);
>  	kmem_cache_free(mmu_page_header_cache, root);
>  }
> @@ -155,6 +162,11 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
>  static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>  				u64 old_spte, u64 new_spte, int level);
>  
> +static int kvm_mmu_page_as_id(struct kvm_mmu_page *sp)
> +{
> +	return sp->role.smm ? 1 : 0;
> +}
> +
>  /**
>   * handle_changed_spte - handle bookkeeping associated with an SPTE change
>   * @kvm: kvm instance
> @@ -262,3 +274,100 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
>  {
>  	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level);
>  }
> +
> +static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
> +				    u64 new_spte)
> +{
> +	u64 *root_pt = tdp_iter_root_pt(iter);
> +	struct kvm_mmu_page *root = sptep_to_sp(root_pt);
> +	int as_id = kvm_mmu_page_as_id(root);
> +
> +	*iter->sptep = new_spte;
> +
> +	handle_changed_spte(kvm, as_id, iter->gfn, iter->old_spte, new_spte,
> +			    iter->level);
> +}
> +
> +#define tdp_root_for_each_pte(_iter, _root, _start, _end) \
> +	for_each_tdp_pte(_iter, _root->spt, _root->role.level, _start, _end)
> +
> +static bool tdp_mmu_iter_cond_resched(struct kvm *kvm, struct tdp_iter *iter)
> +{
> +	if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
> +		kvm_flush_remote_tlbs(kvm);
> +		cond_resched_lock(&kvm->mmu_lock);
> +		tdp_iter_refresh_walk(iter);
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
> +/*
> + * Tears down the mappings for the range of gfns, [start, end), and frees the
> + * non-root pages mapping GFNs strictly within that range. Returns true if
> + * SPTEs have been cleared and a TLB flush is needed before releasing the
> + * MMU lock.
> + */
> +static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> +			  gfn_t start, gfn_t end)
> +{
> +	struct tdp_iter iter;
> +	bool flush_needed = false;
> +
> +	tdp_root_for_each_pte(iter, root, start, end) {
> +		if (!is_shadow_present_pte(iter.old_spte))
> +			continue;
> +
> +		/*
> +		 * If this is a non-last-level SPTE that covers a larger range
> +		 * than should be zapped, continue, and zap the mappings at a
> +		 * lower level.
> +		 */
> +		if ((iter.gfn < start ||
> +		     iter.gfn + KVM_PAGES_PER_HPAGE(iter.level) > end) &&
> +		    !is_last_spte(iter.old_spte, iter.level))
> +			continue;
> +
> +		tdp_mmu_set_spte(kvm, &iter, 0);
> +
> +		flush_needed = !tdp_mmu_iter_cond_resched(kvm, &iter);
> +	}
> +	return flush_needed;
> +}
> +
> +/*
> + * Tears down the mappings for the range of gfns, [start, end), and frees the
> + * non-root pages mapping GFNs strictly within that range. Returns true if
> + * SPTEs have been cleared and a TLB flush is needed before releasing the
> + * MMU lock.
> + */
> +bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end)
> +{
> +	struct kvm_mmu_page *root;
> +	bool flush = false;
> +
> +	for_each_tdp_mmu_root(kvm, root) {
> +		/*
> +		 * Take a reference on the root so that it cannot be freed if
> +		 * this thread releases the MMU lock and yields in this loop.
> +		 */
> +		get_tdp_mmu_root(kvm, root);
> +
> +		flush |= zap_gfn_range(kvm, root, start, end);
> +
> +		put_tdp_mmu_root(kvm, root);
> +	}
> +
> +	return flush;
> +}
> +
> +void kvm_tdp_mmu_zap_all(struct kvm *kvm)
> +{
> +	gfn_t max_gfn = 1ULL << (boot_cpu_data.x86_phys_bits - PAGE_SHIFT);
> +	bool flush;
> +
> +	flush = kvm_tdp_mmu_zap_gfn_range(kvm, 0, max_gfn);
> +	if (flush)
> +		kvm_flush_remote_tlbs(kvm);
> +}
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index ac0ef91294420..6de2d007fc03c 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -12,4 +12,6 @@ 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);
>  
> +bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, gfn_t start, gfn_t end);
> +void kvm_tdp_mmu_zap_all(struct kvm *kvm);
>  #endif /* __KVM_X86_MMU_TDP_MMU_H */
> -- 
> 2.28.0.1011.ga647a8990f-goog
> 

B.R.
Yu