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author | Paolo Bonzini <pbonzini@redhat.com> | 2018-10-23 02:36:47 +0200 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-12-14 12:34:19 +0100 |
commit | 2a31b9db153530df4aa02dac8c32837bf5f47019 (patch) | |
tree | 0cd6fe156ec696e6a55a0d7117794f590ec76958 /arch/mips/kvm | |
parent | 8fe65a8299f9e1f40cb95308ab7b3c4ad80bf801 (diff) | |
download | linux-2a31b9db153530df4aa02dac8c32837bf5f47019.tar.bz2 |
kvm: introduce manual dirty log reprotect
There are two problems with KVM_GET_DIRTY_LOG. First, and less important,
it can take kvm->mmu_lock for an extended period of time. Second, its user
can actually see many false positives in some cases. The latter is due
to a benign race like this:
1. KVM_GET_DIRTY_LOG returns a set of dirty pages and write protects
them.
2. The guest modifies the pages, causing them to be marked ditry.
3. Userspace actually copies the pages.
4. KVM_GET_DIRTY_LOG returns those pages as dirty again, even though
they were not written to since (3).
This is especially a problem for large guests, where the time between
(1) and (3) can be substantial. This patch introduces a new
capability which, when enabled, makes KVM_GET_DIRTY_LOG not
write-protect the pages it returns. Instead, userspace has to
explicitly clear the dirty log bits just before using the content
of the page. The new KVM_CLEAR_DIRTY_LOG ioctl can also operate on a
64-page granularity rather than requiring to sync a full memslot;
this way, the mmu_lock is taken for small amounts of time, and
only a small amount of time will pass between write protection
of pages and the sending of their content.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/mips/kvm')
-rw-r--r-- | arch/mips/kvm/mips.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c index 3898e657952e..3734cd58895e 100644 --- a/arch/mips/kvm/mips.c +++ b/arch/mips/kvm/mips.c @@ -1023,6 +1023,29 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log) return r; } +int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, struct kvm_clear_dirty_log *log) +{ + struct kvm_memslots *slots; + struct kvm_memory_slot *memslot; + bool flush = false; + int r; + + mutex_lock(&kvm->slots_lock); + + r = kvm_clear_dirty_log_protect(kvm, log, &flush); + + if (flush) { + slots = kvm_memslots(kvm); + memslot = id_to_memslot(slots, log->slot); + + /* Let implementation handle TLB/GVA invalidation */ + kvm_mips_callbacks->flush_shadow_memslot(kvm, memslot); + } + + mutex_unlock(&kvm->slots_lock); + return r; +} + long kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) { long r; |