From: Marc Zyngier <maz@kernel.org>
To: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: will@kernel.org, catalin.marinas@arm.com, andrew.jones@linux.dev,
shan.gavin@gmail.com, bgardon@google.com, dmatlack@google.com,
pbonzini@redhat.com, zhenyzha@redhat.com, shuah@kernel.org
Subject: [PATCH v2 1/6] KVM: Use acquire/release semantics when accessing dirty ring GFN state
Date: Mon, 26 Sep 2022 15:51:15 +0100 [thread overview]
Message-ID: <20220926145120.27974-2-maz@kernel.org> (raw)
In-Reply-To: <20220926145120.27974-1-maz@kernel.org>
The current implementation of the dirty ring has an implicit requirement
that stores to the dirty ring from userspace must be:
- be ordered with one another
- visible from another CPU executing a ring reset
While these implicit requirements work well for x86 (and any other
TSO-like architecture), they do not work for more relaxed architectures
such as arm64 where stores to different addresses can be freely
reordered, and loads from these addresses not observing writes from
another CPU unless the required barriers (or acquire/release semantics)
are used.
In order to start fixing this, upgrade the ring reset accesses:
- the kvm_dirty_gfn_harvested() helper now uses acquire semantics
so it is ordered after all previous writes, including that from
userspace
- the kvm_dirty_gfn_set_invalid() helper now uses release semantics
so that the next_slot and next_offset reads don't drift past
the entry invalidation
This is only a partial fix as the userspace side also need upgrading.
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
virt/kvm/dirty_ring.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index f4c2a6eb1666..d6fabf238032 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -74,7 +74,7 @@ int kvm_dirty_ring_alloc(struct kvm_dirty_ring *ring, int index, u32 size)
static inline void kvm_dirty_gfn_set_invalid(struct kvm_dirty_gfn *gfn)
{
- gfn->flags = 0;
+ smp_store_release(&gfn->flags, 0);
}
static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn)
@@ -84,7 +84,7 @@ static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn)
static inline bool kvm_dirty_gfn_harvested(struct kvm_dirty_gfn *gfn)
{
- return gfn->flags & KVM_DIRTY_GFN_F_RESET;
+ return smp_load_acquire(&gfn->flags) & KVM_DIRTY_GFN_F_RESET;
}
int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring)
--
2.34.1
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next prev parent reply other threads:[~2022-09-26 14:51 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-26 14:51 [PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures Marc Zyngier
2022-09-26 14:51 ` Marc Zyngier [this message]
2022-09-26 14:51 ` [PATCH v2 2/6] KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option Marc Zyngier
2022-09-26 14:51 ` [PATCH v2 3/6] KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL Marc Zyngier
2022-09-26 14:51 ` [PATCH v2 4/6] KVM: Document weakly ordered architecture requirements for dirty ring Marc Zyngier
2022-09-26 14:51 ` [PATCH v2 5/6] KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release semantics Marc Zyngier
2022-09-26 14:51 ` [PATCH v2 6/6] KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if available Marc Zyngier
2022-09-27 0:58 ` [PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures Gavin Shan
2022-09-27 15:54 ` Peter Xu
2022-09-29 9:58 ` Marc Zyngier
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