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

[Aurelien Jarno]

On Mon, Nov 30, 2009 at 11:19:06PM +0100, Alexander Graf wrote:
> 
> 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.

If it is sure it is never used, I would prefer to see an abort().
Otherwise it's fine.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net