Re: [Qemu-devel] [PATCH-for-4.2 v2 3/6] s390x/tcg: Flush the TLB of all CPUs on SSKE and RRBE

["Alex Bennée" <alex.bennee@linaro.org>]

David Hildenbrand <david@redhat.com> writes:

> On 14.08.19 12:06, Alex Bennée wrote:
>>
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> Whenever we modify a storage key, we shuld flush the TLBs of all CPUs,
>>> so the MMU fault handling code can properly consider the changed storage
>>> key (to e.g., properly set the reference and change bit on the next
>>> accesses).
>>>
>>> These functions are barely used in modern Linux guests, so the performance
>>> implications are neglectable for now.
>>>
>>> This is a preparation for better reference and change bit handling for
>>> TCG, which will require more MMU changes.
>>>
>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>  target/s390x/mem_helper.c | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
>>> index 29d9eaa5b7..ed54265e03 100644
>>> --- a/target/s390x/mem_helper.c
>>> +++ b/target/s390x/mem_helper.c
>>> @@ -1815,6 +1815,8 @@ void HELPER(sske)(CPUS390XState *env, uint64_t r1, uint64_t r2)
>>>
>>>      key = (uint8_t) r1;
>>>      skeyclass->set_skeys(ss, addr / TARGET_PAGE_SIZE, 1, &key);
>>> +    /* TODO: Flush only entries with this target address */
>>> +    tlb_flush_all_cpus_synced(env_cpu(env));
>>
>> Doesn't:
>>
>>   tlb_flush_page_all_cpus_synced(env_cpu(env), addr & TARGET_PAGE_MASK);
>>
>> do what you want here?
>
> I would have to flush all TLB entries that target this physical page,
> not the entry of the single virtual page. So that does, unfortunately,
> not work.

Ahh I see. Well maybe that should be the comment instead:

  /*
   * As we can only flush by virtual address and not all the entries
   * that point to a physical address we have to flush the whole TLB
   * here.
   */
   tlb_flush_all_cpus_synced(env_cpu(env));

?


--
Alex Bennée