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Message-Id: <20210402005658.3024832-8-seanjc@google.com>
Date: Thu, 1 Apr 2021 17:56:55 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
Paul Mackerras <paulus@...abs.org>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: James Morse <james.morse@....com>,
Julien Thierry <julien.thierry.kdev@...il.com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
linux-mips@...r.kernel.org, kvm@...r.kernel.org,
kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v2 07/10] KVM: Move MMU notifier's mmu_lock acquisition into
common helper
Acquire and release mmu_lock in the __kvm_handle_hva_range() helper
instead of requiring the caller to do the same. This paves the way for
future patches to take mmu_lock if and only if an overlapping memslot is
found, without also having to introduce the on_lock() shenanigans used
to manipulate the notifier count and sequence.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
Note, the WARN_ON_ONCE that asserts on_lock and handler aren't both null
is optimized out of all functions on recent gcc (for x86). I wanted to
make it a BUILD_BUG_ON, but older versions of gcc aren't agressive/smart
enough to optimize it out, and using __builtin_constant_p() to get it to
build on older compilers prevents the assertion from firing on newer
compilers when given bad input.
I'm also a-ok dropping the check altogether, it just felt wrong having
the semi-funky on_lock -> !handler combo without documenting that handler
isn't allowed to be null in the common case.
virt/kvm/kvm_main.c | 125 +++++++++++++++++++++++++++++---------------
1 file changed, 82 insertions(+), 43 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2e809d73c7f1..25ecb5235e17 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -453,28 +453,57 @@ static void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
typedef bool (*hva_handler_t)(struct kvm *kvm, struct kvm_gfn_range *range);
+typedef void (*on_lock_fn_t)(struct kvm *kvm, unsigned long start,
+ unsigned long end);
+
struct kvm_hva_range {
unsigned long start;
unsigned long end;
pte_t pte;
hva_handler_t handler;
+ on_lock_fn_t on_lock;
bool flush_on_ret;
bool may_block;
};
+/*
+ * 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
+ * check for !NULL, whereas comparing against a stub will be elided at compile
+ * time (unless the compiler is getting long in the tooth, e.g. gcc 4.9).
+ */
+static void kvm_null_fn(void)
+{
+
+}
+#define IS_KVM_NULL_FN(fn) ((fn) == (void *)kvm_null_fn)
+
static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
const struct kvm_hva_range *range)
{
- struct kvm_memory_slot *slot;
- struct kvm_memslots *slots;
struct kvm_gfn_range gfn_range;
+ struct kvm_memory_slot *slot;
+ struct kvm_memslots *slots;
bool ret = false;
int i, idx;
- lockdep_assert_held_write(&kvm->mmu_lock);
+ /* 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;
+
+ KVM_MMU_LOCK(kvm);
idx = srcu_read_lock(&kvm->srcu);
+ if (!IS_KVM_NULL_FN(range->on_lock)) {
+ range->on_lock(kvm, range->start, range->end);
+
+ if (IS_KVM_NULL_FN(range->handler))
+ goto out_unlock;
+ }
+
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
kvm_for_each_memslot(slot, slots) {
@@ -510,6 +539,9 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
if (range->flush_on_ret && (ret || kvm->tlbs_dirty))
kvm_flush_remote_tlbs(kvm);
+out_unlock:
+ KVM_MMU_UNLOCK(kvm);
+
srcu_read_unlock(&kvm->srcu, idx);
/* The notifiers are averse to booleans. :-( */
@@ -528,16 +560,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
.end = end,
.pte = pte,
.handler = handler,
+ .on_lock = (void *)kvm_null_fn,
.flush_on_ret = true,
.may_block = false,
};
- int ret;
- KVM_MMU_LOCK(kvm);
- ret = __kvm_handle_hva_range(kvm, &range);
- KVM_MMU_UNLOCK(kvm);
-
- return ret;
+ return __kvm_handle_hva_range(kvm, &range);
}
static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
@@ -551,16 +579,12 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
.end = end,
.pte = __pte(0),
.handler = handler,
+ .on_lock = (void *)kvm_null_fn,
.flush_on_ret = false,
.may_block = false,
};
- int ret;
- KVM_MMU_LOCK(kvm);
- ret = __kvm_handle_hva_range(kvm, &range);
- KVM_MMU_UNLOCK(kvm);
-
- return ret;
+ return __kvm_handle_hva_range(kvm, &range);
}
static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
struct mm_struct *mm,
@@ -581,22 +605,9 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
kvm_handle_hva_range(mn, address, address + 1, pte, kvm_set_spte_gfn);
}
-static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
- const struct mmu_notifier_range *range)
+static void kvm_inc_notifier_count(struct kvm *kvm, unsigned long start,
+ unsigned long end)
{
- struct kvm *kvm = mmu_notifier_to_kvm(mn);
- const struct kvm_hva_range hva_range = {
- .start = range->start,
- .end = range->end,
- .pte = __pte(0),
- .handler = kvm_unmap_gfn_range,
- .flush_on_ret = true,
- .may_block = mmu_notifier_range_blockable(range),
- };
-
- trace_kvm_unmap_hva_range(range->start, range->end);
-
- KVM_MMU_LOCK(kvm);
/*
* The count increase must become visible at unlock time as no
* spte can be established without taking the mmu_lock and
@@ -604,8 +615,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
*/
kvm->mmu_notifier_count++;
if (likely(kvm->mmu_notifier_count == 1)) {
- kvm->mmu_notifier_range_start = range->start;
- kvm->mmu_notifier_range_end = range->end;
+ kvm->mmu_notifier_range_start = start;
+ kvm->mmu_notifier_range_end = end;
} else {
/*
* Fully tracking multiple concurrent ranges has dimishing
@@ -617,24 +628,36 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
* complete.
*/
kvm->mmu_notifier_range_start =
- min(kvm->mmu_notifier_range_start, range->start);
+ min(kvm->mmu_notifier_range_start, start);
kvm->mmu_notifier_range_end =
- max(kvm->mmu_notifier_range_end, range->end);
+ max(kvm->mmu_notifier_range_end, end);
}
-
- __kvm_handle_hva_range(kvm, &hva_range);
-
- KVM_MMU_UNLOCK(kvm);
-
- return 0;
}
-static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
+static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
const struct mmu_notifier_range *range)
{
struct kvm *kvm = mmu_notifier_to_kvm(mn);
+ const struct kvm_hva_range hva_range = {
+ .start = range->start,
+ .end = range->end,
+ .pte = __pte(0),
+ .handler = kvm_unmap_gfn_range,
+ .on_lock = kvm_inc_notifier_count,
+ .flush_on_ret = true,
+ .may_block = mmu_notifier_range_blockable(range),
+ };
- KVM_MMU_LOCK(kvm);
+ trace_kvm_unmap_hva_range(range->start, range->end);
+
+ __kvm_handle_hva_range(kvm, &hva_range);
+
+ return 0;
+}
+
+static void kvm_dec_notifier_count(struct kvm *kvm, unsigned long start,
+ unsigned long end)
+{
/*
* This sequence increase will notify the kvm page fault that
* the page that is going to be mapped in the spte could have
@@ -648,7 +671,23 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
* in conjunction with the smp_rmb in mmu_notifier_retry().
*/
kvm->mmu_notifier_count--;
- KVM_MMU_UNLOCK(kvm);
+}
+
+static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
+ const struct mmu_notifier_range *range)
+{
+ struct kvm *kvm = mmu_notifier_to_kvm(mn);
+ const struct kvm_hva_range hva_range = {
+ .start = range->start,
+ .end = range->end,
+ .pte = __pte(0),
+ .handler = (void *)kvm_null_fn,
+ .on_lock = kvm_dec_notifier_count,
+ .flush_on_ret = true,
+ .may_block = mmu_notifier_range_blockable(range),
+ };
+
+ __kvm_handle_hva_range(kvm, &hva_range);
BUG_ON(kvm->mmu_notifier_count < 0);
}
--
2.31.0.208.g409f899ff0-goog
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