On Wed, Jan 27, 2010 at 03:54:08PM +0100, Jan Kiszka wrote:
> This patch originates in the mp_state writeback issue: During runtime
> and even on reset, we must not write the previously saved VCPU state
> back into the kernel in an uncontrolled fashion. E.g mp_state should
> only written on reset or on VCPU setup. Certain clocks (e.g. the TSC)
> may only be written on setup or after vmload.
>
> By introducing additional information about the context of the planned
> vcpu state manipulation, we can simply skip sensitive states like
> mp_state when updating the in-kernel state. The planned modifications
> are defined when calling cpu_synchronize_state. They accumulate, ie.
> once a full writeback was requested, it will stick until it was
> performed.
>
> This patch already fixes existing writeback issues in upstream KVM by
> only selectively writing MSR_IA32_TSC, MSR_KVM_SYSTEM_TIME,
> MSR_KVM_WALL_CLOCK, the mp_state and the vcpu_events.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
>
> This patch is intentionally written against uq/master. As upstream is
> less convoluted (yet :) ), it may help understanding the basic idea. An
> add-on patch for qemu-kvm that both cleans up the current code and also
> moves kvm_get/set_lapic into kvm_arch_get/put_registers (hmm, maybe also
> renaming that services...) will follow soon if no one sees fundamental
> problems of this approach.
>
> exec.c | 4 ++--
> gdbstub.c | 10 +++++-----
> hw/apic.c | 2 +-
> hw/ppc_newworld.c | 2 +-
> hw/ppc_oldworld.c | 2 +-
> hw/s390-virtio.c | 2 +-
> kvm-all.c | 31 +++++++++++++++++++------------
> kvm.h | 13 +++++++++----
> monitor.c | 4 ++--
> target-i386/helper.c | 2 +-
> target-i386/kvm.c | 31 +++++++++++++++++++------------
> target-i386/machine.c | 4 ++--
> target-ppc/kvm.c | 2 +-
> target-ppc/machine.c | 4 ++--
> target-s390x/kvm.c | 17 ++++++++++++-----
> 15 files changed, 78 insertions(+), 52 deletions(-)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index f8350c9..8595cd9 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -57,7 +57,8 @@ struct KVMState
> KVMSlot slots[32];
> int fd;
> int vmfd;
> - int regs_modified;
> + int synchronized;
> + int pending_modifications;
> int coalesced_mmio;
> #ifdef KVM_CAP_COALESCED_MMIO
> struct kvm_coalesced_mmio_ring *coalesced_mmio_ring;
Should be per-vcpu.
> @@ -155,10 +156,12 @@ static void kvm_reset_vcpu(void *opaque)
> CPUState *env = opaque;
>
> kvm_arch_reset_vcpu(env);
> - if (kvm_arch_put_registers(env)) {
> + if (kvm_arch_put_registers(env, env->kvm_state->pending_modifications
> + | CPU_MODIFY_RESET)) {
> fprintf(stderr, "Fatal: kvm vcpu reset failed\n");
> abort();
> }
> + env->kvm_state->pending_modifications = CPU_MODIFY_NONE;
Can't the writeback here happen at exec_cpu?
> @@ -946,9 +953,9 @@ static void kvm_invoke_set_guest_debug(void *data)
> struct kvm_set_guest_debug_data *dbg_data = data;
> CPUState *env = dbg_data->env;
>
> - if (env->kvm_state->regs_modified) {
> - kvm_arch_put_registers(env);
> - env->kvm_state->regs_modified = 0;
> + if (env->kvm_state->pending_modifications) {
> + kvm_arch_put_registers(env, env->kvm_state->pending_modifications);
> + env->kvm_state->pending_modifications = CPU_MODIFY_NONE;
> }
Why's synchronous writeback needed here?
Otherwise seems fine.
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