diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/kvm_host.h | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index cf761ff58224..5e1cb74922b3 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -48,6 +48,27 @@ */ #define KVM_MEMSLOT_INVALID (1UL << 16) +/* + * Bit 0 of the memslot generation number is an "update in-progress flag", + * e.g. is temporarily set for the duration of install_new_memslots(). + * This flag effectively creates a unique generation number that is used to + * mark cached memslot data, e.g. MMIO accesses, as potentially being stale, + * i.e. may (or may not) have come from the previous memslots generation. + * + * This is necessary because the actual memslots update is not atomic with + * respect to the generation number update. Updating the generation number + * first would allow a vCPU to cache a spte from the old memslots using the + * new generation number, and updating the generation number after switching + * to the new memslots would allow cache hits using the old generation number + * to reference the defunct memslots. + * + * This mechanism is used to prevent getting hits in KVM's caches while a + * memslot update is in-progress, and to prevent cache hits *after* updating + * the actual generation number against accesses that were inserted into the + * cache *before* the memslots were updated. + */ +#define KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS BIT_ULL(0) + /* Two fragments for cross MMIO pages. */ #define KVM_MAX_MMIO_FRAGMENTS 2 |