Commit cec29eef authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: Add a dedicated mmu_notifier flag for reclaiming freed memory 



Handle AMD SEV's kvm_arch_guest_memory_reclaimed() hook by having
__kvm_handle_hva_range() return whether or not an overlapping memslot
was found, i.e. mmu_lock was acquired.  Using the .on_unlock() hook
works, but kvm_arch_guest_memory_reclaimed() needs to run after dropping
mmu_lock, which makes .on_lock() and .on_unlock() asymmetrical.

Use a small struct to return the tuple of the notifier-specific return,
plus whether or not overlap was found.  Because the iteration helpers are
__always_inlined, practically speaking, the struct will never actually be
returned from a function call (not to mention the size of the struct will
be two bytes in practice).

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarFuad Tabba <tabba@google.com>
Tested-by: default avatarFuad Tabba <tabba@google.com>
Message-Id: <20231027182217.3615211-11-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 16f95f3b

virt/kvm/kvm_main.c

+37 −16
Original line number Diff line number Diff line
@@ -561,6 +561,19 @@ struct kvm_mmu_notifier_range { 
	bool may_block;

};



/*

 * The inner-most helper returns a tuple containing the return value from the

 * arch- and action-specific handler, plus a flag indicating whether or not at

 * least one memslot was found, i.e. if the handler found guest memory.

 *

 * Note, most notifiers are averse to booleans, so even though KVM tracks the

 * return from arch code as a bool, outer helpers will cast it to an int. :-(

 */

typedef struct kvm_mmu_notifier_return {

	bool ret;

	bool found_memslot;

} kvm_mn_ret_t;



/*

 * Use a dedicated stub instead of NULL to indicate that there is no callback

 * function/handler.  The compiler technically can't guarantee that a real
@@ -582,22 +595,25 @@ static const union kvm_mmu_notifier_arg KVM_MMU_NOTIFIER_NO_ARG; 
	     node;							     \

	     node = interval_tree_iter_next(node, start, last))	     \



static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,

static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,

							   const struct kvm_mmu_notifier_range *range)

{

	bool ret = false, locked = false;

	struct kvm_mmu_notifier_return r = {

		.ret = false,

		.found_memslot = false,

	};

	struct kvm_gfn_range gfn_range;

	struct kvm_memory_slot *slot;

	struct kvm_memslots *slots;

	int i, idx;



	if (WARN_ON_ONCE(range->end <= range->start))

		return 0;

		return r;



	/* A null handler is allowed if and only if on_lock() is provided. */

	if (WARN_ON_ONCE(IS_KVM_NULL_FN(range->on_lock) &&

			 IS_KVM_NULL_FN(range->handler)))

		return 0;

		return r;



	idx = srcu_read_lock(&kvm->srcu);
@@ -631,8 +647,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, 
			gfn_range.end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, slot);

			gfn_range.slot = slot;



			if (!locked) {

				locked = true;

			if (!r.found_memslot) {

				r.found_memslot = true;

				KVM_MMU_LOCK(kvm);

				if (!IS_KVM_NULL_FN(range->on_lock))

					range->on_lock(kvm);
@@ -640,14 +656,14 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, 
				if (IS_KVM_NULL_FN(range->handler))

					break;

			}

			ret |= range->handler(kvm, &gfn_range);

			r.ret |= range->handler(kvm, &gfn_range);

		}

	}



	if (range->flush_on_ret && ret)

	if (range->flush_on_ret && r.ret)

		kvm_flush_remote_tlbs(kvm);



	if (locked) {

	if (r.found_memslot) {

		KVM_MMU_UNLOCK(kvm);

		if (!IS_KVM_NULL_FN(range->on_unlock))

			range->on_unlock(kvm);
@@ -655,8 +671,7 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm, 


	srcu_read_unlock(&kvm->srcu, idx);



	/* The notifiers are averse to booleans. :-( */

	return (int)ret;

	return r;

}



static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
@@ -677,7 +692,7 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn, 
		.may_block	= false,

	};



	return __kvm_handle_hva_range(kvm, &range);

	return __kvm_handle_hva_range(kvm, &range).ret;

}



static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
@@ -696,7 +711,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn 
		.may_block	= false,

	};



	return __kvm_handle_hva_range(kvm, &range);

	return __kvm_handle_hva_range(kvm, &range).ret;

}



static bool kvm_change_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
@@ -798,7 +813,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, 
		.end		= range->end,

		.handler	= kvm_mmu_unmap_gfn_range,

		.on_lock	= kvm_mmu_invalidate_begin,

		.on_unlock	= kvm_arch_guest_memory_reclaimed,

		.on_unlock	= (void *)kvm_null_fn,

		.flush_on_ret	= true,

		.may_block	= mmu_notifier_range_blockable(range),

	};
@@ -830,7 +845,13 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn, 
	gfn_to_pfn_cache_invalidate_start(kvm, range->start, range->end,

					  hva_range.may_block);



	__kvm_handle_hva_range(kvm, &hva_range);

	/*

	 * If one or more memslots were found and thus zapped, notify arch code

	 * that guest memory has been reclaimed.  This needs to be done *after*

	 * dropping mmu_lock, as x86's reclaim path is slooooow.

	 */

	if (__kvm_handle_hva_range(kvm, &hva_range).found_memslot)

		kvm_arch_guest_memory_reclaimed(kvm);



	return 0;

}