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authorSean Christopherson <seanjc@google.com>2023-10-27 20:21:52 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2023-11-13 11:31:37 +0100
commitcec29eef0a815386d520d61c2cbe16d537931639 (patch)
tree1821e7d4a62f39e239e776021372c8461542d909
parentKVM: Add KVM_EXIT_MEMORY_FAULT exit to report faults to userspace (diff)
downloadlinux-cec29eef0a815386d520d61c2cbe16d537931639.tar.xz
linux-cec29eef0a815386d520d61c2cbe16d537931639.zip
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: 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>
-rw-r--r--virt/kvm/kvm_main.c53
1 files changed, 37 insertions, 16 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 756b94ecd511..e18a7f152c0b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -562,6 +562,19 @@ struct kvm_mmu_notifier_range {
};
/*
+ * 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
* function will have a non-zero address, and so it will generate code to
@@ -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,
- const struct kvm_mmu_notifier_range *range)
+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;
}