Make fast_page_fault interoperate with the TDP MMU by leveraging
walk_shadow_page_lockless_{begin,end} to acquire the RCU read lock and
introducing a new helper function kvm_tdp_mmu_get_last_sptep_lockless to
grab the lowest level sptep.
Suggested-by: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 55 +++++++++++++++++++++++++++-----------
arch/x86/kvm/mmu/tdp_mmu.c | 36 +++++++++++++++++++++++++
arch/x86/kvm/mmu/tdp_mmu.h | 2 ++
3 files changed, 78 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 88c71a8a55f1..1d410278a4cc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3105,15 +3105,45 @@ static bool is_access_allowed(u32 fault_err_code, u64 spte)
return spte & PT_PRESENT_MASK;
}
+/*
+ * Returns the last level spte pointer of the shadow page walk for the given
+ * gpa, and sets *spte to the spte value. This spte may be non-preset.
+ *
+ * If no walk could be performed, returns NULL and *spte does not contain valid
+ * data.
+ *
+ * Constraints:
+ * - Must be called between walk_shadow_page_lockless_{begin,end}.
+ * - The returned sptep must not be used after walk_shadow_page_lockless_end.
+ */
+u64 *get_last_sptep_lockless(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte)
+{
+ struct kvm_shadow_walk_iterator iterator;
+ u64 old_spte;
+ u64 *sptep = NULL;
+
+ if (is_tdp_mmu(vcpu->arch.mmu))
+ return kvm_tdp_mmu_get_last_sptep_lockless(vcpu, gpa, spte);
+
+ for_each_shadow_entry_lockless(vcpu, gpa, iterator, old_spte) {
+ sptep = iterator.sptep;
+ *spte = old_spte;
+
+ if (!is_shadow_present_pte(old_spte))
+ break;
+ }
+
+ return sptep;
+}
+
/*
* Returns one of RET_PF_INVALID, RET_PF_FIXED or RET_PF_SPURIOUS.
*/
static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
{
- struct kvm_shadow_walk_iterator iterator;
- struct kvm_mmu_page *sp;
int ret = RET_PF_INVALID;
u64 spte = 0ull;
+ u64 *sptep = NULL;
uint retry_count = 0;
if (!page_fault_can_be_fast(error_code))
@@ -3122,16 +3152,14 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
walk_shadow_page_lockless_begin(vcpu);
do {
+ struct kvm_mmu_page *sp;
u64 new_spte;
- for_each_shadow_entry_lockless(vcpu, gpa, iterator, spte)
- if (!is_shadow_present_pte(spte))
- break;
-
+ sptep = get_last_sptep_lockless(vcpu, gpa, &spte);
if (!is_shadow_present_pte(spte))
break;
- sp = sptep_to_sp(iterator.sptep);
+ sp = sptep_to_sp(sptep);
if (!is_last_spte(spte, sp->role.level))
break;
@@ -3189,8 +3217,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
* since the gfn is not stable for indirect shadow page. See
* Documentation/virt/kvm/locking.rst to get more detail.
*/
- if (fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte,
- new_spte)) {
+ if (fast_pf_fix_direct_spte(vcpu, sp, sptep, spte, new_spte)) {
ret = RET_PF_FIXED;
break;
}
@@ -3203,7 +3230,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code)
} while (true);
- trace_fast_page_fault(vcpu, gpa, error_code, iterator.sptep, spte, ret);
+ trace_fast_page_fault(vcpu, gpa, error_code, sptep, spte, ret);
walk_shadow_page_lockless_end(vcpu);
return ret;
@@ -3838,11 +3865,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (page_fault_handle_page_track(vcpu, error_code, gfn))
return RET_PF_EMULATE;
- if (!is_tdp_mmu_fault) {
- r = fast_page_fault(vcpu, gpa, error_code);
- if (r != RET_PF_INVALID)
- return r;
- }
+ r = fast_page_fault(vcpu, gpa, error_code);
+ if (r != RET_PF_INVALID)
+ return r;
r = mmu_topup_memory_caches(vcpu, false);
if (r)
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index c6fa8d00bf9f..2c9e0ed71fa0 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -527,6 +527,10 @@ static inline bool tdp_mmu_set_spte_atomic_no_dirty_log(struct kvm *kvm,
if (is_removed_spte(iter->old_spte))
return false;
+ /*
+ * TDP MMU sptes can also be concurrently cmpxchg'd in
+ * fast_pf_fix_direct_spte as part of fast_page_fault.
+ */
if (cmpxchg64(rcu_dereference(iter->sptep), iter->old_spte,
new_spte) != iter->old_spte)
return false;
@@ -1546,3 +1550,35 @@ int kvm_tdp_mmu_get_walk_lockless(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
return leaf;
}
+
+/*
+ * Must be called between kvm_tdp_mmu_walk_shadow_page_lockless_{begin,end}.
+ *
+ * The returned sptep must not be used after
+ * kvm_tdp_mmu_walk_shadow_page_lockless_end.
+ */
+u64 *kvm_tdp_mmu_get_last_sptep_lockless(struct kvm_vcpu *vcpu, u64 addr,
+ u64 *spte)
+{
+ struct tdp_iter iter;
+ struct kvm_mmu *mmu = vcpu->arch.mmu;
+ gfn_t gfn = addr >> PAGE_SHIFT;
+ tdp_ptep_t sptep = NULL;
+
+ tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) {
+ *spte = iter.old_spte;
+ sptep = iter.sptep;
+ }
+
+ if (sptep)
+ /*
+ * Perform the rcu dereference here since we are passing the
+ * sptep up to the generic MMU code which does not know the
+ * synchronization details of the TDP MMU. This is safe as long
+ * as the caller obeys the contract that the sptep is not used
+ * after kvm_tdp_mmu_walk_shadow_page_lockless_end.
+ */
+ return rcu_dereference(sptep);
+
+ return NULL;
+}
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index e9dde5f9c0ef..508a23bdf7da 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -81,6 +81,8 @@ void kvm_tdp_mmu_walk_lockless_begin(void);
void kvm_tdp_mmu_walk_lockless_end(void);
int kvm_tdp_mmu_get_walk_lockless(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
int *root_level);
+u64 *kvm_tdp_mmu_get_last_sptep_lockless(struct kvm_vcpu *vcpu, u64 addr,
+ u64 *spte);
#ifdef CONFIG_X86_64
bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);
--
2.32.0.93.g670b81a890-goog
