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KVM: Add a dedicated mmu_notifier flag for reclaiming freed memory

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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: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Message-Id: <20231027182217.3615211-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-10-27 11:21:52 -07:00 committed by Paolo Bonzini
parent 16f95f3b95
commit cec29eef0a
1 changed files with 37 additions and 16 deletions
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51
virt/kvm/kvm_main.c
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@ -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;
}