KVM: PPC: Book3S HV: Provide a method for userspace to read and write the HPT

A new ioctl, KVM_PPC_GET_HTAB_FD, returns a file descriptor.  Reads on
this fd return the contents of the HPT (hashed page table), writes
create and/or remove entries in the HPT.  There is a new capability,
KVM_CAP_PPC_HTAB_FD, to indicate the presence of the ioctl.  The ioctl
takes an argument structure with the index of the first HPT entry to
read out and a set of flags.  The flags indicate whether the user is
intending to read or write the HPT, and whether to return all entries
or only the "bolted" entries (those with the bolted bit, 0x10, set in
the first doubleword).

This is intended for use in implementing qemu's savevm/loadvm and for
live migration.  Therefore, on reads, the first pass returns information
about all HPTEs (or all bolted HPTEs).  When the first pass reaches the
end of the HPT, it returns from the read.  Subsequent reads only return
information about HPTEs that have changed since they were last read.
A read that finds no changed HPTEs in the HPT following where the last
read finished will return 0 bytes.

The format of the data provides a simple run-length compression of the
invalid entries.  Each block of data starts with a header that indicates
the index (position in the HPT, which is just an array), the number of
valid entries starting at that index (may be zero), and the number of
invalid entries following those valid entries.  The valid entries, 16
bytes each, follow the header.  The invalid entries are not explicitly
represented.

Signed-off-by: Paul Mackerras <paulus@samba.org>
[agraf: fix documentation]
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 494a84c37c3e..e6e5d4b13708 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -634,6 +634,7 @@ struct kvm_ppc_smmu_info {
 #endif
 #define KVM_CAP_IRQFD_RESAMPLE 82
 #define KVM_CAP_PPC_BOOKE_WATCHDOG 83
+#define KVM_CAP_PPC_HTAB_FD 84
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -859,6 +860,8 @@ struct kvm_s390_ucas_mapping {
 #define KVM_CREATE_SPAPR_TCE	  _IOW(KVMIO,  0xa8, struct kvm_create_spapr_tce)
 /* Available with KVM_CAP_RMA */
 #define KVM_ALLOCATE_RMA	  _IOR(KVMIO,  0xa9, struct kvm_allocate_rma)
+/* Available with KVM_CAP_PPC_HTAB_FD */
+#define KVM_PPC_GET_HTAB_FD	  _IOW(KVMIO,  0xaa, struct kvm_get_htab_fd)
 
 /*
  * ioctls for vcpu fds