Commit 6e8eb206 authored by David Matlack's avatar David Matlack Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: fast_page_fault support for the TDP MMU 



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_fast_pf_get_last_sptep to
grab the lowest level sptep.

Suggested-by: default avatarBen Gardon <bgardon@google.com>
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Message-Id: <20210713220957.3493520-5-dmatlack@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c5c8c7c5

arch/x86/kvm/mmu/mmu.c

+37 −13
Original line number Diff line number Diff line
@@ -3108,15 +3108,41 @@ 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.

 *

 * Contract:

 *  - Must be called between walk_shadow_page_lockless_{begin,end}.

 *  - The returned sptep must not be used after walk_shadow_page_lockless_end.

 */

static u64 *fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte)

{

	struct kvm_shadow_walk_iterator iterator;

	u64 old_spte;

	u64 *sptep = NULL;



	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))
@@ -3127,14 +3153,15 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code) 
	do {

		u64 new_spte;



		for_each_shadow_entry_lockless(vcpu, gpa, iterator, spte)

			if (!is_shadow_present_pte(spte))

				break;

		if (is_tdp_mmu(vcpu->arch.mmu))

			sptep = kvm_tdp_mmu_fast_pf_get_last_sptep(vcpu, gpa, &spte);

		else

			sptep = fast_pf_get_last_sptep(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;
@@ -3192,8 +3219,7 @@ 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;

		}
@@ -3206,7 +3232,7 @@ 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;
@@ -3841,11 +3867,9 @@ 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 = mmu_topup_memory_caches(vcpu, false);

	if (r)

arch/x86/kvm/mmu/tdp_mmu.c

+41 −0
Original line number Diff line number Diff line
@@ -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;



	/*

	 * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and

	 * does not hold the mmu_lock.

	 */

	if (cmpxchg64(rcu_dereference(iter->sptep), iter->old_spte,

		      new_spte) != iter->old_spte)

		return false;
@@ -1536,3 +1540,40 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, 


	return leaf;

}



/*

 * 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.

 *

 * Contract:

 *  - Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}.

 *  - The returned sptep must not be used after kvm_tdp_mmu_walk_lockless_end.

 *

 * WARNING: This function is only intended to be called during fast_page_fault.

 */

u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(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;

	}



	/*

	 * Perform the rcu_dereference to get the raw spte pointer value since

	 * we are passing it up to fast_page_fault, which is shared with the

	 * legacy MMU and thus does not retain the TDP MMU-specific __rcu

	 * annotation.

	 *

	 * This is safe since fast_page_fault obeys the contracts of this

	 * function as well as all TDP MMU contracts around modifying SPTEs

	 * outside of mmu_lock.

	 */

	return rcu_dereference(sptep);

}

arch/x86/kvm/mmu/tdp_mmu.h

+2 −0
Original line number Diff line number Diff line
@@ -89,6 +89,8 @@ static inline void kvm_tdp_mmu_walk_lockless_end(void) 


int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,

			 int *root_level);

u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,

					u64 *spte);



#ifdef CONFIG_X86_64

bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);