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| author | Paolo Bonzini <pbonzini@redhat.com> | 2022-10-03 15:33:32 -0400 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-10-03 15:33:32 -0400 |
| commit | fe4d9e4abf622598bd199d0805d20afa12f70c92 (patch) | |
| tree | ccb8d2aff2c311be6a316a77c1955a8dac9749b8 /Documentation/virt | |
| parent | e779ce9d17c44a338b4fa3be8715e3b7eb9706f0 (diff) | |
| parent | b302ca52ba8235ff0e18c0fa1fa92b51784aef6a (diff) | |
Merge tag 'kvmarm-6.1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
KVM/arm64 updates for v6.1
- Fixes for single-stepping in the presence of an async
exception as well as the preservation of PSTATE.SS
- Better handling of AArch32 ID registers on AArch64-only
systems
- Fixes for the dirty-ring API, allowing it to work on
architectures with relaxed memory ordering
- Advertise the new kvmarm mailing list
- Various minor cleanups and spelling fixes
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 236a797be71c..eee9f857a986 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7918,8 +7918,8 @@ guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf (0x40000001). Otherwise, a guest may use the paravirtual features regardless of what has actually been exposed through the CPUID leaf. -8.29 KVM_CAP_DIRTY_LOG_RING ---------------------------- +8.29 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL +---------------------------------------------------------- :Architectures: x86 :Parameters: args[0] - size of the dirty log ring @@ -7977,6 +7977,11 @@ on to the next GFN. The userspace should continue to do this until the flags of a GFN have the DIRTY bit cleared, meaning that it has harvested all the dirty GFNs that were available. +Note that on weakly ordered architectures, userspace accesses to the +ring buffer (and more specifically the 'flags' field) must be ordered, +using load-acquire/store-release accessors when available, or any +other memory barrier that will ensure this ordering. + It's not necessary for userspace to harvest the all dirty GFNs at once. However it must collect the dirty GFNs in sequence, i.e., the userspace program cannot skip one dirty GFN to collect the one next to it. @@ -8005,6 +8010,14 @@ KVM_CAP_DIRTY_LOG_RING with an acceptable dirty ring size, the virtual machine will switch to ring-buffer dirty page tracking and further KVM_GET_DIRTY_LOG or KVM_CLEAR_DIRTY_LOG ioctls will fail. +NOTE: KVM_CAP_DIRTY_LOG_RING_ACQ_REL is the only capability that +should be exposed by weakly ordered architecture, in order to indicate +the additional memory ordering requirements imposed on userspace when +reading the state of an entry and mutating it from DIRTY to HARVESTED. +Architecture with TSO-like ordering (such as x86) are allowed to +expose both KVM_CAP_DIRTY_LOG_RING and KVM_CAP_DIRTY_LOG_RING_ACQ_REL +to userspace. + 8.30 KVM_CAP_XEN_HVM -------------------- |