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

[Thomas Huth <thuth@redhat.com>]

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.

Reviewed-by: Thomas Huth <thuth@redhat.com>