Re: [Qemu-devel] [qemu-s390x] [PATCH-for-4.2 v2 6/6] s390x/mmu: Factor out storage key handling

[David Hildenbrand <david@redhat.com>]

On 14.08.19 20:01, Thomas Huth wrote:
> On 8/14/19 9:23 AM, David Hildenbrand wrote:
>> Factor it out, add a comment how it all works, and also use it in the
>> REAL MMU.
>>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  target/s390x/mmu_helper.c | 113 +++++++++++++++++++++++---------------
>>  1 file changed, 69 insertions(+), 44 deletions(-)
>>
>> diff --git a/target/s390x/mmu_helper.c b/target/s390x/mmu_helper.c
>> index 6cc81a29b6..e125837d68 100644
>> --- a/target/s390x/mmu_helper.c
>> +++ b/target/s390x/mmu_helper.c
>> @@ -334,6 +334,73 @@ static int mmu_translate_asce(CPUS390XState *env, target_ulong vaddr,
>>      return r;
>>  }
>>  
>> +static void mmu_handle_skey(target_ulong addr, int rw, int *flags)
>> +{
>> +    static S390SKeysClass *skeyclass;
>> +    static S390SKeysState *ss;
>> +    uint8_t key;
>> +    int rc;
>> +
>> +    if (unlikely(!ss)) {
>> +        ss = s390_get_skeys_device();
>> +        skeyclass = S390_SKEYS_GET_CLASS(ss);
>> +    }
>> +
>> +    /*
>> +     * Whenever we create a new TLB entry, we set the storage key reference
>> +     * bit. In case we allow write accesses, we set the storage key change
>> +     * bit. Whenever the guest changes the storage key, we have to flush the
>> +     * TLBs of all CPUs (the whole TLB or all affected entries), so that the
>> +     * next reference/change will result in an MMU fault and make us properly
>> +     * update the storage key here.
>> +     *
>> +     * Note 1: "record of references ... is not necessarily accurate",
>> +     *         "change bit may be set in case no storing has occurred".
>> +     *         -> We can set reference/change bits even on exceptions.
>> +     * Note 2: certain accesses seem to ignore storage keys. For example,
>> +     *         DAT translation does not set reference bits for table accesses.
>> +     *
>> +     * TODO: key-controlled protection. Only CPU accesses make use of the
>> +     *       PSW key. CSS accesses are different - we have to pass in the key.
>> +     *
>> +     * TODO: we have races between getting and setting the key.
>> +     */
>> +    if (addr < ram_size) {
> 
> If you want to get rid of some indentation, you could do an early return
> if (addr >= ram_size) here instead.

Right, that makes a lot of sense, will do this. Thanks!

> 
> Anyway, good idea to refactor this code, so also in its current shape:
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> 


-- 

Thanks,

David / dhildenb