Commit f47e5bbb authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap 



Re-introduce zapping only leaf SPTEs in kvm_zap_gfn_range() and
kvm_tdp_mmu_unmap_gfn_range(), this time without losing a pending TLB
flush when processing multiple roots (including nested TDP shadow roots).
Dropping the TLB flush resulted in random crashes when running Hyper-V
Server 2019 in a guest with KSM enabled in the host (or any source of
mmu_notifier invalidations, KSM is just the easiest to force).

This effectively revert commits 873dd122
and fcb93eb6, and thus restores commit
cf3e2642, plus this delta on top:

bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end,
        struct kvm_mmu_page *root;

        for_each_tdp_mmu_root_yield_safe(kvm, root, as_id)
-               flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, false);
+               flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, flush);

        return flush;
 }

Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Tested-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220325230348.2587437-1-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a80ced6e

arch/x86/kvm/mmu/mmu.c

+2 −2
Original line number Diff line number Diff line
@@ -5849,8 +5849,8 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end) 


	if (is_tdp_mmu_enabled(kvm)) {

		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)

			flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start,

							  gfn_end, flush);

			flush = kvm_tdp_mmu_zap_leafs(kvm, i, gfn_start,

						      gfn_end, true, flush);

	}



	if (flush)

arch/x86/kvm/mmu/tdp_mmu.c

+16 −39
Original line number Diff line number Diff line
@@ -909,10 +909,8 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp) 
}



/*

 * 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.

 * Zap leafs SPTEs for the range of gfns, [start, end). Returns true if SPTEs

 * have been cleared and a TLB flush is needed before releasing the MMU lock.

 *

 * If can_yield is true, will release the MMU lock and reschedule if the

 * scheduler needs the CPU or there is contention on the MMU lock. If this
@@ -920,42 +918,25 @@ bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp) 
 * the caller must ensure it does not supply too large a GFN range, or the

 * operation can cause a soft lockup.

 */

static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,

static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,

			      gfn_t start, gfn_t end, bool can_yield, bool flush)

{

	bool zap_all = (start == 0 && end >= tdp_mmu_max_gfn_host());

	struct tdp_iter iter;



	/*

	 * No need to try to step down in the iterator when zapping all SPTEs,

	 * zapping the top-level non-leaf SPTEs will recurse on their children.

	 */

	int min_level = zap_all ? root->role.level : PG_LEVEL_4K;



	end = min(end, tdp_mmu_max_gfn_host());



	lockdep_assert_held_write(&kvm->mmu_lock);



	rcu_read_lock();



	for_each_tdp_pte_min_level(iter, root, min_level, start, end) {

	for_each_tdp_pte_min_level(iter, root, PG_LEVEL_4K, start, end) {

		if (can_yield &&

		    tdp_mmu_iter_cond_resched(kvm, &iter, flush, false)) {

			flush = false;

			continue;

		}



		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, except when zapping all SPTEs.

		 */

		if (!zap_all &&

		    (iter.gfn < start ||

		     iter.gfn + KVM_PAGES_PER_HPAGE(iter.level) > end) &&

		if (!is_shadow_present_pte(iter.old_spte) ||

		    !is_last_spte(iter.old_spte, iter.level))

			continue;
@@ -963,17 +944,13 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
		flush = true;

	}



	/*

	 * Need to flush before releasing RCU.  TODO: do it only if intermediate

	 * page tables were zapped; there is no need to flush under RCU protection

	 * if no 'struct kvm_mmu_page' is freed.

	 */

	if (flush)

		kvm_flush_remote_tlbs_with_address(kvm, start, end - start);



	rcu_read_unlock();



	return false;

	/*

	 * Because this flow zaps _only_ leaf SPTEs, the caller doesn't need

	 * to provide RCU protection as no 'struct kvm_mmu_page' will be freed.

	 */

	return flush;

}



/*
@@ -982,13 +959,13 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, 
 * 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, int as_id, gfn_t start,

				 gfn_t end, bool can_yield, bool flush)

bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end,

			   bool can_yield, bool flush)

{

	struct kvm_mmu_page *root;



	for_each_tdp_mmu_root_yield_safe(kvm, root, as_id)

		flush = zap_gfn_range(kvm, root, start, end, can_yield, flush);

		flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, flush);



	return flush;

}
@@ -1236,7 +1213,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) 
bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,

				 bool flush)

{

	return __kvm_tdp_mmu_zap_gfn_range(kvm, range->slot->as_id, range->start,

	return kvm_tdp_mmu_zap_leafs(kvm, range->slot->as_id, range->start,

				     range->end, range->may_block, flush);

}

arch/x86/kvm/mmu/tdp_mmu.h

+1 −7
Original line number Diff line number Diff line
@@ -15,14 +15,8 @@ __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root) 
void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,

			  bool shared);



bool __kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id, gfn_t start,

bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start,

				 gfn_t end, bool can_yield, bool flush);

static inline bool kvm_tdp_mmu_zap_gfn_range(struct kvm *kvm, int as_id,

					     gfn_t start, gfn_t end, bool flush)

{

	return __kvm_tdp_mmu_zap_gfn_range(kvm, as_id, start, end, true, flush);

}



bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp);

void kvm_tdp_mmu_zap_all(struct kvm *kvm);

void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm);