• Paul Mackerras's avatar
    KVM: PPC: Add support for Book3S processors in hypervisor mode · de56a948
    Paul Mackerras authored
    This adds support for KVM running on 64-bit Book 3S processors,
    specifically POWER7, in hypervisor mode.  Using hypervisor mode means
    that the guest can use the processor's supervisor mode.  That means
    that the guest can execute privileged instructions and access privileged
    registers itself without trapping to the host.  This gives excellent
    performance, but does mean that KVM cannot emulate a processor
    architecture other than the one that the hardware implements.
    
    This code assumes that the guest is running paravirtualized using the
    PAPR (Power Architecture Platform Requirements) interface, which is the
    interface that IBM's PowerVM hypervisor uses.  That means that existing
    Linux distributions that run on IBM pSeries machines will also run
    under KVM without modification.  In order to communicate the PAPR
    hypercalls to qemu, this adds a new KVM_EXIT_PAPR_HCALL exit code
    to include/linux/kvm.h.
    
    Currently the choice between book3s_hv support and book3s_pr support
    (i.e. the existing code, which runs the guest in user mode) has to be
    made at kernel configuration time, so a given kernel binary can only
    do one or the other.
    
    This new book3s_hv code doesn't support MMIO emulation at present.
    Since we are running paravirtualized guests, this isn't a serious
    restriction.
    
    With the guest running in supervisor mode, most exceptions go straight
    to the guest.  We will never get data or instruction storage or segment
    interrupts, alignment interrupts, decrementer interrupts, program
    interrupts, single-step interrupts, etc., coming to the hypervisor from
    the guest.  Therefore this introduces a new KVMTEST_NONHV macro for the
    exception entry path so that we don't have to do the KVM test on entry
    to those exception handlers.
    
    We do however get hypervisor decrementer, hypervisor data storage,
    hypervisor instruction storage, and hypervisor emulation assist
    interrupts, so we have to handle those.
    
    In hypervisor mode, real-mode accesses can access all of RAM, not just
    a limited amount.  Therefore we put all the guest state in the vcpu.arch
    and use the shadow_vcpu in the PACA only for temporary scratch space.
    We allocate the vcpu with kzalloc rather than vzalloc, and we don't use
    anything in the kvmppc_vcpu_book3s struct, so we don't allocate it.
    We don't have a shared page with the guest, but we still need a
    kvm_vcpu_arch_shared struct to store the values of various registers,
    so we include one in the vcpu_arch struct.
    
    The POWER7 processor has a restriction that all threads in a core have
    to be in the same partition.  MMU-on kernel code counts as a partition
    (partition 0), so we have to do a partition switch on every entry to and
    exit from the guest.  At present we require the host and guest to run
    in single-thread mode because of this hardware restriction.
    
    This code allocates a hashed page table for the guest and initializes
    it with HPTEs for the guest's Virtual Real Memory Area (VRMA).  We
    require that the guest memory is allocated using 16MB huge pages, in
    order to simplify the low-level memory management.  This also means that
    we can get away without tracking paging activity in the host for now,
    since huge pages can't be paged or swapped.
    
    This also adds a few new exports needed by the book3s_hv code.
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
    de56a948
book3s_exports.c 1.18 KB