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Diffstat (limited to 'Documentation/virt/kvm/api.rst')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index ebd383fba939..0adef66585b1 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5707,8 +5707,13 @@ and injected exceptions. :Architectures: x86, arm, arm64, mips :Parameters: args[0] whether feature should be enabled or not -With this capability enabled, KVM_GET_DIRTY_LOG will not automatically -clear and write-protect all pages that are returned as dirty. +Valid flags are:: + + #define KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (1 << 0) + #define KVM_DIRTY_LOG_INITIALLY_SET (1 << 1) + +With KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE is set, KVM_GET_DIRTY_LOG will not +automatically clear and write-protect all pages that are returned as dirty. Rather, userspace will have to do this operation separately using KVM_CLEAR_DIRTY_LOG. @@ -5719,12 +5724,19 @@ than requiring to sync a full memslot; this ensures that KVM does not take spinlocks for an extended period of time. Second, in some cases a large amount of time can pass between a call to KVM_GET_DIRTY_LOG and userspace actually using the data in the page. Pages can be modified -during this time, which is inefficint for both the guest and userspace: +during this time, which is inefficient for both the guest and userspace: the guest will incur a higher penalty due to write protection faults, while userspace can see false reports of dirty pages. Manual reprotection helps reducing this time, improving guest performance and reducing the number of dirty log false positives. +With KVM_DIRTY_LOG_INITIALLY_SET set, all the bits of the dirty bitmap +will be initialized to 1 when created. This also improves performance because +dirty logging can be enabled gradually in small chunks on the first call +to KVM_CLEAR_DIRTY_LOG. KVM_DIRTY_LOG_INITIALLY_SET depends on +KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE (it is also only available on +x86 for now). + KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make it hard or impossible to use it correctly. The availability of |