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Diffstat (limited to 'arch/x86/kvm/mmu/tdp_mmu.c')
-rw-r--r--arch/x86/kvm/mmu/tdp_mmu.c154
1 files changed, 93 insertions, 61 deletions
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 953082bf96..04c1f0957f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -149,11 +149,11 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
* If shared is set, this function is operating under the MMU lock in read
* mode.
*/
-#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _only_valid)\
- for (_root = tdp_mmu_next_root(_kvm, NULL, _only_valid); \
- ({ lockdep_assert_held(&(_kvm)->mmu_lock); }), _root; \
- _root = tdp_mmu_next_root(_kvm, _root, _only_valid)) \
- if (kvm_mmu_page_as_id(_root) != _as_id) { \
+#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _only_valid) \
+ for (_root = tdp_mmu_next_root(_kvm, NULL, _only_valid); \
+ ({ lockdep_assert_held(&(_kvm)->mmu_lock); }), _root; \
+ _root = tdp_mmu_next_root(_kvm, _root, _only_valid)) \
+ if (_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) { \
} else
#define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id) \
@@ -171,12 +171,19 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
* Holding mmu_lock for write obviates the need for RCU protection as the list
* is guaranteed to be stable.
*/
-#define for_each_tdp_mmu_root(_kvm, _root, _as_id) \
- list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link) \
- if (kvm_lockdep_assert_mmu_lock_held(_kvm, false) && \
- kvm_mmu_page_as_id(_root) != _as_id) { \
+#define __for_each_tdp_mmu_root(_kvm, _root, _as_id, _only_valid) \
+ list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link) \
+ if (kvm_lockdep_assert_mmu_lock_held(_kvm, false) && \
+ ((_as_id >= 0 && kvm_mmu_page_as_id(_root) != _as_id) || \
+ ((_only_valid) && (_root)->role.invalid))) { \
} else
+#define for_each_tdp_mmu_root(_kvm, _root, _as_id) \
+ __for_each_tdp_mmu_root(_kvm, _root, _as_id, false)
+
+#define for_each_valid_tdp_mmu_root(_kvm, _root, _as_id) \
+ __for_each_tdp_mmu_root(_kvm, _root, _as_id, true)
+
static struct kvm_mmu_page *tdp_mmu_alloc_sp(struct kvm_vcpu *vcpu)
{
struct kvm_mmu_page *sp;
@@ -216,22 +223,41 @@ static void tdp_mmu_init_child_sp(struct kvm_mmu_page *child_sp,
tdp_mmu_init_sp(child_sp, iter->sptep, iter->gfn, role);
}
-hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
+int kvm_tdp_mmu_alloc_root(struct kvm_vcpu *vcpu)
{
- union kvm_mmu_page_role role = vcpu->arch.mmu->root_role;
+ struct kvm_mmu *mmu = vcpu->arch.mmu;
+ union kvm_mmu_page_role role = mmu->root_role;
+ int as_id = kvm_mmu_role_as_id(role);
struct kvm *kvm = vcpu->kvm;
struct kvm_mmu_page *root;
- lockdep_assert_held_write(&kvm->mmu_lock);
+ /*
+ * Check for an existing root before acquiring the pages lock to avoid
+ * unnecessary serialization if multiple vCPUs are loading a new root.
+ * E.g. when bringing up secondary vCPUs, KVM will already have created
+ * a valid root on behalf of the primary vCPU.
+ */
+ read_lock(&kvm->mmu_lock);
+
+ for_each_valid_tdp_mmu_root_yield_safe(kvm, root, as_id) {
+ if (root->role.word == role.word)
+ goto out_read_unlock;
+ }
+
+ spin_lock(&kvm->arch.tdp_mmu_pages_lock);
/*
- * Check for an existing root before allocating a new one. Note, the
- * role check prevents consuming an invalid root.
+ * Recheck for an existing root after acquiring the pages lock, another
+ * vCPU may have raced ahead and created a new usable root. Manually
+ * walk the list of roots as the standard macros assume that the pages
+ * lock is *not* held. WARN if grabbing a reference to a usable root
+ * fails, as the last reference to a root can only be put *after* the
+ * root has been invalidated, which requires holding mmu_lock for write.
*/
- for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {
+ list_for_each_entry(root, &kvm->arch.tdp_mmu_roots, link) {
if (root->role.word == role.word &&
- kvm_tdp_mmu_get_root(root))
- goto out;
+ !WARN_ON_ONCE(!kvm_tdp_mmu_get_root(root)))
+ goto out_spin_unlock;
}
root = tdp_mmu_alloc_sp(vcpu);
@@ -245,13 +271,20 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
* is ultimately put by kvm_tdp_mmu_zap_invalidated_roots().
*/
refcount_set(&root->tdp_mmu_root_count, 2);
-
- spin_lock(&kvm->arch.tdp_mmu_pages_lock);
list_add_rcu(&root->link, &kvm->arch.tdp_mmu_roots);
- spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
-out:
- return __pa(root->spt);
+out_spin_unlock:
+ spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
+out_read_unlock:
+ read_unlock(&kvm->mmu_lock);
+ /*
+ * Note, KVM_REQ_MMU_FREE_OBSOLETE_ROOTS will prevent entering the guest
+ * and actually consuming the root if it's invalidated after dropping
+ * mmu_lock, and the root can't be freed as this vCPU holds a reference.
+ */
+ mmu->root.hpa = __pa(root->spt);
+ mmu->root.pgd = 0;
+ return 0;
}
static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
@@ -734,15 +767,26 @@ static void tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
rcu_read_lock();
/*
- * To avoid RCU stalls due to recursively removing huge swaths of SPs,
- * split the zap into two passes. On the first pass, zap at the 1gb
- * level, and then zap top-level SPs on the second pass. "1gb" is not
- * arbitrary, as KVM must be able to zap a 1gb shadow page without
- * inducing a stall to allow in-place replacement with a 1gb hugepage.
+ * Zap roots in multiple passes of decreasing granularity, i.e. zap at
+ * 4KiB=>2MiB=>1GiB=>root, in order to better honor need_resched() (all
+ * preempt models) or mmu_lock contention (full or real-time models).
+ * Zapping at finer granularity marginally increases the total time of
+ * the zap, but in most cases the zap itself isn't latency sensitive.
*
- * Because zapping a SP recurses on its children, stepping down to
- * PG_LEVEL_4K in the iterator itself is unnecessary.
+ * If KVM is configured to prove the MMU, skip the 4KiB and 2MiB zaps
+ * in order to mimic the page fault path, which can replace a 1GiB page
+ * table with an equivalent 1GiB hugepage, i.e. can get saddled with
+ * zapping a 1GiB region that's fully populated with 4KiB SPTEs. This
+ * allows verifying that KVM can safely zap 1GiB regions, e.g. without
+ * inducing RCU stalls, without relying on a relatively rare event
+ * (zapping roots is orders of magnitude more common). Note, because
+ * zapping a SP recurses on its children, stepping down to PG_LEVEL_4K
+ * in the iterator itself is unnecessary.
*/
+ if (!IS_ENABLED(CONFIG_KVM_PROVE_MMU)) {
+ __tdp_mmu_zap_root(kvm, root, shared, PG_LEVEL_4K);
+ __tdp_mmu_zap_root(kvm, root, shared, PG_LEVEL_2M);
+ }
__tdp_mmu_zap_root(kvm, root, shared, PG_LEVEL_1G);
__tdp_mmu_zap_root(kvm, root, shared, root->role.level);
@@ -800,7 +844,13 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
continue;
tdp_mmu_iter_set_spte(kvm, &iter, 0);
- flush = true;
+
+ /*
+ * Zappings SPTEs in invalid roots doesn't require a TLB flush,
+ * see kvm_tdp_mmu_zap_invalidated_roots() for details.
+ */
+ if (!root->role.invalid)
+ flush = true;
}
rcu_read_unlock();
@@ -813,16 +863,16 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
}
/*
- * Zap leaf SPTEs for the range of gfns, [start, end), for all roots. Returns
- * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or
- * more SPTEs were zapped since the MMU lock was last acquired.
+ * Zap leaf SPTEs for the range of gfns, [start, end), for all *VALID** roots.
+ * Returns true if a TLB flush is needed before releasing the MMU lock, i.e. if
+ * one or more SPTEs were zapped since the MMU lock was last acquired.
*/
bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, gfn_t start, gfn_t end, bool flush)
{
struct kvm_mmu_page *root;
lockdep_assert_held_write(&kvm->mmu_lock);
- for_each_tdp_mmu_root_yield_safe(kvm, root)
+ for_each_valid_tdp_mmu_root_yield_safe(kvm, root, -1)
flush = tdp_mmu_zap_leafs(kvm, root, start, end, true, flush);
return flush;
@@ -896,7 +946,7 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
* the VM is being destroyed).
*
* Note, kvm_tdp_mmu_zap_invalidated_roots() is gifted the TDP MMU's reference.
- * See kvm_tdp_mmu_get_vcpu_root_hpa().
+ * See kvm_tdp_mmu_alloc_root().
*/
void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm)
{
@@ -1508,13 +1558,6 @@ static bool tdp_mmu_need_write_protect(struct kvm_mmu_page *sp)
return kvm_mmu_page_ad_need_write_protect(sp) || !kvm_ad_enabled();
}
-/*
- * Clear the dirty status of all the SPTEs mapping GFNs in the memslot. If
- * AD bits are enabled, this will involve clearing the dirty bit on each SPTE.
- * If AD bits are not enabled, this will require clearing the writable bit on
- * each SPTE. Returns true if an SPTE has been changed and the TLBs need to
- * be flushed.
- */
static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
gfn_t start, gfn_t end)
{
@@ -1551,11 +1594,9 @@ retry:
}
/*
- * Clear the dirty status of all the SPTEs mapping GFNs in the memslot. If
- * AD bits are enabled, this will involve clearing the dirty bit on each SPTE.
- * If AD bits are not enabled, this will require clearing the writable bit on
- * each SPTE. Returns true if an SPTE has been changed and the TLBs need to
- * be flushed.
+ * Clear the dirty status (D-bit or W-bit) of all the SPTEs mapping GFNs in the
+ * memslot. Returns true if an SPTE has been changed and the TLBs need to be
+ * flushed.
*/
bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm,
const struct kvm_memory_slot *slot)
@@ -1571,13 +1612,6 @@ bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm,
return spte_set;
}
-/*
- * Clears the dirty status of all the 4k SPTEs mapping GFNs for which a bit is
- * set in mask, starting at gfn. The given memslot is expected to contain all
- * the GFNs represented by set bits in the mask. If AD bits are enabled,
- * clearing the dirty status will involve clearing the dirty bit on each SPTE
- * or, if AD bits are not enabled, clearing the writable bit on each SPTE.
- */
static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
gfn_t gfn, unsigned long mask, bool wrprot)
{
@@ -1620,11 +1654,9 @@ static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
}
/*
- * Clears the dirty status of all the 4k SPTEs mapping GFNs for which a bit is
- * set in mask, starting at gfn. The given memslot is expected to contain all
- * the GFNs represented by set bits in the mask. If AD bits are enabled,
- * clearing the dirty status will involve clearing the dirty bit on each SPTE
- * or, if AD bits are not enabled, clearing the writable bit on each SPTE.
+ * Clear the dirty status (D-bit or W-bit) of all the 4k SPTEs mapping GFNs for
+ * which a bit is set in mask, starting at gfn. The given memslot is expected to
+ * contain all the GFNs represented by set bits in the mask.
*/
void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
@@ -1633,7 +1665,7 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
{
struct kvm_mmu_page *root;
- for_each_tdp_mmu_root(kvm, root, slot->as_id)
+ for_each_valid_tdp_mmu_root(kvm, root, slot->as_id)
clear_dirty_pt_masked(kvm, root, gfn, mask, wrprot);
}
@@ -1751,7 +1783,7 @@ bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
bool spte_set = false;
lockdep_assert_held_write(&kvm->mmu_lock);
- for_each_tdp_mmu_root(kvm, root, slot->as_id)
+ for_each_valid_tdp_mmu_root(kvm, root, slot->as_id)
spte_set |= write_protect_gfn(kvm, root, gfn, min_level);
return spte_set;