Re: [Qemu-devel] [PATCH 06/11] Add support for S390x system emulation

[Alexander Graf]

On 30.11.2009, at 19:18, Aurelien Jarno wrote:

> On Thu, Nov 26, 2009 at 02:23:15PM +0100, Alexander Graf wrote:
>> Let's enable the basics for system emulation so we can run virtual machines
>> with KVM!
> 
> I don't really understand while this whole patch is not merged in patch
> number 1. Otherwise, please find the comments below.

Historical reasons. To keep Uli's stripped down version separate from my code.

> 
>> Signed-off-by: Alexander Graf <address@hidden>
>> ---
>> target-s390x/cpu.h                |  153 
>> ++++++++++++++++++++++++++++++++++++-
>> target-s390x/exec.h               |    5 +
>> target-s390x/helper.c             |   22 +++++
>> target-s390x/machine.c            |   30 +++++++
>> 4 files changed, 208 insertions(+), 2 deletions(-)
>> create mode 100644 default-configs/s390x-softmmu.mak
>> create mode 100644 target-s390x/machine.c
>> 
>> diff --git a/default-configs/s390x-softmmu.mak 
>> b/default-configs/s390x-softmmu.mak
>> new file mode 100644
>> index 0000000..e69de29
>> diff --git a/target-s390x/cpu.h b/target-s390x/cpu.h
>> index f45b00c..a74745c 100644
>> --- a/target-s390x/cpu.h
>> +++ b/target-s390x/cpu.h
>> @@ -30,8 +30,7 @@
>> 
>> #include "softfloat.h"
>> 
>> -#define NB_MMU_MODES 2 // guess
>> -#define MMU_USER_IDX 0 // guess
>> +#define NB_MMU_MODES 2
>> 
>> typedef union FPReg {
>>     struct {
>> @@ -77,6 +76,15 @@ static inline void cpu_clone_regs(CPUState *env, 
>> target_ulong newsp)
>> }
>> #endif
>> 
>> +#define MMU_MODE0_SUFFIX _kernel
>> +#define MMU_MODE1_SUFFIX _user
>> +#define MMU_USER_IDX 1
>> +static inline int cpu_mmu_index (CPUState *env)
>> +{
>> +    /* XXX: Currently we don't implement virtual memory */
>> +    return 0;
> 
> Is it correct? It means that memory access will aways be kernel memory
> accesses. IIRC, even with KVM enabled, softmmu accesses are possible in
> some cases (devices ?).

I can't imagine any hardware using the CPU's MMU to write to RAM. That's what 
IOMMUs are for.

The only 2 consumers are:

1) tcg
2) gdb / monitor

With 2) being broken, because we can't resolve virtual addresses to physical 
addresses. But that won't change until someone implements the softmmu emulation 
target for real.