Re: [Qemu-devel] [PATCH 3/3] s390x/helper: Added format control bit to MMU translation

[Thomas Huth]

On Fri, 25 Apr 2014 14:36:11 +0200
Alexander Graf <address@hidden> wrote:
> 
> On 25.04.14 14:15, Thomas Huth wrote:
> >
> > On Thu, 24 Apr 2014 18:36:18 +0200
> > Alexander Graf <address@hidden> wrote:
[...]
> >> I also think we should rather align the
> >> code with the PTE handling somehow. This way it gets pretty confusing to
> >> follow. How about something like this (untested)?
> > I gave it a try ... works fine with two small modifications...
> >
> >> diff --git a/target-s390x/helper.c b/target-s390x/helper.c
> >> index aa628b8..96c1c66 100644
> >> --- a/target-s390x/helper.c
> >> +++ b/target-s390x/helper.c
> >> @@ -170,6 +170,48 @@ static void trigger_page_fault(CPUS390XState *env,
> >> target_ulong vaddr,
> >>        trigger_pgm_exception(env, type, ilen);
> >>    }
> >>
> >> +static int mmu_translate_pte(CPUS390XState *env, target_ulong vaddr,
> >> +                             uint64_t asc, uint64_t asce,
> >> +                              target_ulong *raddr, int *flags, int rw)
> >> +{
> >> +    if (asce & _PAGE_INVALID) {
> >> +        DPRINTF("%s: PTE=0x%" PRIx64 " invalid\n", __func__, asce);
> >> +        trigger_page_fault(env, vaddr, PGM_PAGE_TRANS, asc, rw);
> >> +        return -1;
> >> +    }
> >> +
> >> +    if (asce & _PAGE_RO) {
> >> +        *flags &= ~PAGE_WRITE;
> >> +    }
> >> +
> >> +    *raddr = asce & _ASCE_ORIGIN;
> >> +
> >> +    PTE_DPRINTF("%s: PTE=0x%" PRIx64 "\n", __func__, asce);
> >> +
> >> +    return 0;
> >> +}
> >> +
> >> +static int mmu_translate_segpte(CPUS390XState *env, target_ulong vaddr,
> >> +                                uint64_t asc, uint64_t asce,
> >> +                                 target_ulong *raddr, int *flags, int rw)
> >> +{
> >> +    if (asce & _SEGMENT_ENTRY_INV) {
> >> +        DPRINTF("%s: SEG=0x%" PRIx64 " invalid\n", __func__, asce);
> >> +        trigger_page_fault(env, vaddr, PGM_SEGMENT_TRANS, asc, rw);
> >> +        return -1;
> >> +    }
> >> +
> >> +    if (asce & _PAGE_RO) { /* XXX is this correct? */
> > You can remove the XXX comment, the protection bit is the same for
> > both, page table entries and segment table entries.
> >
> >> +        *flags &= ~PAGE_WRITE;
> >> +    }
> >> +
> >> +    *raddr = (asce & 0xfffffffffff00000ULL) | (vaddr & 0xfffff);
> >> +
> >> +    PTE_DPRINTF("%s: SEG=0x%" PRIx64 "\n", __func__, asce);
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>    static int mmu_translate_asce(CPUS390XState *env, target_ulong vaddr,
> >>                                  uint64_t asc, uint64_t asce, int level,
> >>                                  target_ulong *raddr, int *flags, int rw)
> >> @@ -229,28 +271,19 @@ static int mmu_translate_asce(CPUS390XState *env,
> >> target_ulong vaddr,
> >>        PTE_DPRINTF("%s: 0x%" PRIx64 " + 0x%" PRIx64 " => 0x%016" PRIx64 
> >> "\n",
> >>                    __func__, origin, offs, new_asce);
> >>
> >> -    if (level != _ASCE_TYPE_SEGMENT) {
> >> +    } if (level == _ASCE_TYPE_SEGMENT) {
> > I had to remove the "}" at the beginning of above line.
> >
> >> +        /* 4KB page */
> >> +        return mmu_translate_pte(env, vaddr, asc, new_asce, raddr,
> >> flags, rw);
> >> +    } else if (((level - 4) == _ASCE_TYPE_SEGMENT) &&
> >> +               (env->cregs[0] & CR0_EDAT) &&
> >> +        (asce & _SEGMENT_ENTRY_FC)) {
> > That's got to be "(new_asce & _SEGMENT_ENTRY_FC)" instead.
> >
> >> +        /* 1MB page */
> >> +        return mmu_translate_segpte(env, vaddr, asc, new_asce, raddr,
> >> flags, rw);
> >> +    } else {
> >>            /* yet another region */
> >>            return mmu_translate_asce(env, vaddr, asc, new_asce, level -
> >> 4, raddr,
> >>                                      flags, rw);
> >>        }
> >> -
> >> -    /* PTE */
> >> -    if (new_asce & _PAGE_INVALID) {
> >> -        DPRINTF("%s: PTE=0x%" PRIx64 " invalid\n", __func__, new_asce);
> >> -        trigger_page_fault(env, vaddr, PGM_PAGE_TRANS, asc, rw);
> >> -        return -1;
> >> -    }
> >> -
> >> -    if (new_asce & _PAGE_RO) {
> >> -        *flags &= ~PAGE_WRITE;
> >> -    }
> >> -
> >> -    *raddr = new_asce & _ASCE_ORIGIN;
> >> -
> >> -    PTE_DPRINTF("%s: PTE=0x%" PRIx64 "\n", __func__, new_asce);
> >> -
> >> -    return 0;
> >>    }
> >>
> >>    static int mmu_translate_asc(CPUS390XState *env, target_ulong vaddr,
> > I'm fine with these changes, too. So how shall we continue? Could you
> > assemble a complete patch or shall I prepare one?
> 
> You go ahead and do one. If you can think of a good way to combine 
> mmu_translate_pte and mmu_translate_seg into a single function I'd be 
> happy to see that too :).
> 
> With the RO flag identical the only differences left are the page mask 
> (4k is implicit for QEMU's TLB, that's why it's omitted for normal PTEs) 
> and the page fault injection. Do 1MB PTEs fault with a page fault or a 
> segment fault? If they fault with a page fault, it's probably the best 
> to just have one mmu_translate_pte() function with a mask parameter.

No, you always get segment translation exceptions instead. And there is
another difference: The entry-is-invalid bit is at a different location
(_PAGE_INVALID vs. _SEGMENT_ENTRY_INV). So I think it's nicer to keep
the functions separated instead of adding too much if-statements or
functions parameters there, ok?

 Thomas