On 03/26/2018 11:20 AM, David Hildenbrand wrote:
> Manually having to use cpu_synchronize_state() is error prone. I don't
> think that the performance impact is that huge if we simply synchronize
> the state on every kvm_arch_handle_exit() call. This makes the code
> easier to maintain.
>
> We now also call it (although not neded) for
> - KVM_EXIT_S390_RESET -> s390_reipl_request()
> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
> - unmanagable/unimplemented intercepts
> - ICPT_WAITPSW -> s390_handle_wait() -> cpu gets halted
> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
> - Scenarios where we inject an operation exception
> - handle_sigp() on the source CPU
> - handle_stsi()
>
> I don't think any of these are performance critical. Especially as we
> have all information directly contained in kvm_run, there are no
> additional IOCTLs to issue on modern kernels.
We had other issues in the past in other (common code) places. For example
see
commit 79ca7a1b898eb97c4192f3c78027a0f20485e7b4
Author: Christian Borntraeger <borntrae...@de.ibm.com>
AuthorDate: Tue Mar 7 15:19:08 2017 +0100
Commit: Paolo Bonzini <pbonz...@redhat.com>
CommitDate: Tue Mar 14 13:26:36 2017 +0100
exec: add cpu_synchronize_state to cpu_memory_rw_debug
so we might consider going even further.....But this will be tricky.
FWIW, I think your patch even fixes a bug:
--- snip ----
static int handle_diag(S390CPU *cpu, struct kvm_run *run, uint32_t ipb)
{
int r = 0;
uint16_t func_code;
/*
* For any diagnose call we support, bits 48-63 of the resulting
* address specify the function code; the remainder is ignored.
*/
func_code = decode_basedisp_rs(&cpu->env, ipb, NULL) & DIAG_KVM_CODE_MASK;
---->
static inline hwaddr decode_basedisp_s(CPUS390XState *env, uint32_t ipb,
uint8_t *ar)
{
hwaddr addr = 0;
uint8_t reg;
reg = ipb >> 28;
if (reg > 0) {
addr = env->regs[reg];
----> we do the sync_regs after this in the diag handler!
So currently we only handle the case with base reg == 0 correctly.
So
diag x,y,0x500(0)
works
but things like
lghi 1,0x500
diag x,y,0(1)
not unless I miss something.
[...]
> @@ -1778,6 +1760,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run
> *run)
>
> qemu_mutex_lock_iothread();
>
> + cpu_synchronize_state(CPU(cpu));
> +
> switch (run->exit_reason) {
> case KVM_EXIT_S390_SIEIC:
> ret = handle_intercept(cpu);
>
Does it make sense to do this hunk NOW for 2.12 (cc stable)
and queue your full patch for 2.13?
