Re: [PATCH v1 07/12] s390x/mmu_helper: move address validation into mmu_translate*()

[Thomas Huth <thuth@redhat.com>]

On 06/08/2021 10.20, David Hildenbrand wrote:
> On 06.08.21 10:18, Thomas Huth wrote:
>> On 05/08/2021 17.27, David Hildenbrand wrote:
>>> Let's move address validation into mmu_translate() and
>>> mmu_translate_real(). This allows for checking whether an absolute
>>> address is valid before looking up the storage key. We can now get rid of
>>> the ram_size check.
>>>
>>> Interestingly, we're already handling LOAD REAL ADDRESS wrong, because
>>> a) We're not supposed to touch storage keys
>>> b) We're not supposed to convert to an absolute address
>>>
>>> Let's use a fake, negative MMUAccessType to teach mmu_translate() to
>>> fix that handling and to not perform address validation.
>>>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>    target/s390x/mmu_helper.c      | 36 ++++++++++++++++++++--------------
>>>    target/s390x/tcg/excp_helper.c | 13 ------------
>>>    target/s390x/tcg/mem_helper.c  |  2 +-
>>>    3 files changed, 22 insertions(+), 29 deletions(-)
>>>
>>> diff --git a/target/s390x/mmu_helper.c b/target/s390x/mmu_helper.c
>>> index ca25dadb5b..36ab4e9c81 100644
>>> --- a/target/s390x/mmu_helper.c
>>> +++ b/target/s390x/mmu_helper.c
>>> @@ -301,14 +301,13 @@ static void mmu_handle_skey(target_ulong addr, int 
>>> rw, int *flags)
>>>    {
>>>        static S390SKeysClass *skeyclass;
>>>        static S390SKeysState *ss;
>>> -    MachineState *ms = MACHINE(qdev_get_machine());
>>>        uint8_t key;
>>>        int rc;
>>> -    if (unlikely(addr >= ms->ram_size)) {
>>> -        return;
>>> -    }
>>> -
>>> +    /*
>>> +     * We excpect to be called with an absolute address that has already 
>>> been
>>> +     * validated, such that we can reliably use it to lookup the storage 
>>> key.
>>> +     */
>>>        if (unlikely(!ss)) {
>>>            ss = s390_get_skeys_device();
>>>            skeyclass = S390_SKEYS_GET_CLASS(ss);
>>> @@ -370,7 +369,7 @@ static void mmu_handle_skey(target_ulong addr, int 
>>> rw, int *flags)
>>>    /**
>>>     * Translate a virtual (logical) address into a physical (absolute) 
>>> address.
>>>     * @param vaddr  the virtual address
>>> - * @param rw     0 = read, 1 = write, 2 = code fetch
>>> + * @param rw     0 = read, 1 = write, 2 = code fetch, < 0 = load real 
>>> address
>>>     * @param asc    address space control (one of the PSW_ASC_* modes)
>>>     * @param raddr  the translated address is stored to this pointer
>>>     * @param flags  the PAGE_READ/WRITE/EXEC flags are stored to this 
>>> pointer
>>> @@ -449,10 +448,17 @@ int mmu_translate(CPUS390XState *env, target_ulong 
>>> vaddr, int rw, uint64_t asc,
>>>        }
>>>    nodat:
>>> -    /* Convert real address -> absolute address */
>>> -    *raddr = mmu_real2abs(env, *raddr);
>>> +    if (rw >= 0) {
>>> +        /* Convert real address -> absolute address */
>>> +        *raddr = mmu_real2abs(env, *raddr);
>>> -    mmu_handle_skey(*raddr, rw, flags);
>>> +        if (!mmu_absolute_addr_valid(*raddr, rw == MMU_DATA_STORE)) {
>>> +            *tec = 0; /* unused */
>>> +            return PGM_ADDRESSING;
>>> +        }
>>> +
>>> +        mmu_handle_skey(*raddr, rw, flags);
>>> +    }
>>>        return 0;
>>>    }
>>> @@ -473,12 +479,6 @@ static int translate_pages(S390CPU *cpu, vaddr addr, 
>>> int nr_pages,
>>>            if (ret) {
>>>                return ret;
>>>            }
>>> -        if (!address_space_access_valid(&address_space_memory, pages[i],
>>> -                                        TARGET_PAGE_SIZE, is_write,
>>> -                                        MEMTXATTRS_UNSPECIFIED)) {
>>> -            *tec = 0; /* unused */
>>> -            return PGM_ADDRESSING;
>>> -        }
>>>            addr += TARGET_PAGE_SIZE;
>>>        }
>>> @@ -588,6 +588,12 @@ int mmu_translate_real(CPUS390XState *env, 
>>> target_ulong raddr, int rw,
>>>        *addr = mmu_real2abs(env, raddr & TARGET_PAGE_MASK);
>>> +    if (!mmu_absolute_addr_valid(*addr, rw == MMU_DATA_STORE)) {
>>> +        /* unused */
>>> +        *tec = 0;
>>> +        return PGM_ADDRESSING;
>>> +    }
>>> +
>>>        mmu_handle_skey(*addr, rw, flags);
>>>        return 0;
>>>    }
>>> diff --git a/target/s390x/tcg/excp_helper.c b/target/s390x/tcg/excp_helper.c
>>> index a61917d04f..3d6662a53c 100644
>>> --- a/target/s390x/tcg/excp_helper.c
>>> +++ b/target/s390x/tcg/excp_helper.c
>>> @@ -150,19 +150,6 @@ bool s390_cpu_tlb_fill(CPUState *cs, vaddr address, 
>>> int size,
>>>            g_assert_not_reached();
>>>        }
>>> -    /* check out of RAM access */
>>> -    if (!excp &&
>>> -        !address_space_access_valid(&address_space_memory, raddr,
>>> -                                    TARGET_PAGE_SIZE, access_type,
>>> -                                    MEMTXATTRS_UNSPECIFIED)) {
>>> -        MachineState *ms = MACHINE(qdev_get_machine());
>>> -        qemu_log_mask(CPU_LOG_MMU,
>>> -                      "%s: raddr %" PRIx64 " > ram_size %" PRIx64 "\n",
>>> -                      __func__, (uint64_t)raddr, (uint64_t)ms->ram_size);
>>> -        excp = PGM_ADDRESSING;
>>> -        tec = 0; /* unused */
>>> -    }
>>> -
>>>        env->tlb_fill_exc = excp;
>>>        env->tlb_fill_tec = tec;
>>> diff --git a/target/s390x/tcg/mem_helper.c b/target/s390x/tcg/mem_helper.c
>>> index a84795cfa3..9c1b9c7d06 100644
>>> --- a/target/s390x/tcg/mem_helper.c
>>> +++ b/target/s390x/tcg/mem_helper.c
>>> @@ -2456,7 +2456,7 @@ uint64_t HELPER(lra)(CPUS390XState *env, uint64_t 
>>> addr)
>>>            tcg_s390_program_interrupt(env, PGM_SPECIAL_OP, GETPC());
>>>        }
>>> -    exc = mmu_translate(env, addr, 0, asc, &ret, &flags, &tec);
>>> +    exc = mmu_translate(env, addr, -1, asc, &ret, &flags, &tec);
>>
>> Do we maybe want a #define for this -1 instead? OTOH, you've added a proper
>> comment to the function description, so that should be ok, too.
> 
> Ideally, I'd have used a completely new MMU_* type. But affecting all users 
> in QEMU for one special case and having to handle it consequently 
> accordingly all over the place feels wrong.
> 
> Where would you put the define?

I agree that this should not go into the common header ... so maybe into 
s390x-internal.h ?

  Thomas