Re: [Qemu-devel] [PATCH RFC 0/3] s390x/tcg: LAP support using immediate TLB invalidation

[David Hildenbrand <david@redhat.com>]

On 29.09.2017 13:49, Cornelia Huck wrote:
> On Wed, 27 Sep 2017 19:00:24 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
>> Details about Low-Address Protection can be found in description of
>> patch 1 and 2. It is basically a subpage protection of the first two
>> pages of every address space (for which it is enabled).
>>
>> We can achieve this by simply directly invalidating the TLB entry and
>> therefore forcing every write accesses onto these two pages into the slow
>> path.
>>
>> With this patch, I can boot Linux just fine (which uses LAP). This also
>> makes all related kvm-unit-tests that we have pass.
>>
>> The checks are working that good, that I discovered a STFL bug. STFL
>> stores into the low addresses but low-address protection does explicitly
>> not apply. The Linux kernel calls STFL while LAP is active. So without
>> patch nr 3, booting Linux will fail. (this change is also part of a patch
>> of my SMP series).
> 
> I fear I have lost track a bit with all those patches floating around.
> IIUC, patch 3 fixes a real bug that is only exposed by your LAP
> changes. It used to be part of the stfl changes in v1 of your smp
> series but is no longer in v2. So, is this a patch that can be applied
> to current s390-next?
> 

The SMP series is based on both, this series and the CPU cleanup series
you already picked up.

You can apply Patch 3 with the following modified description (requested
by Thomas):


s390x/tcg: make STFL store into the lowcore

Using virtual memory access is wrong and will soon include low-address
protection checks, which is to be bypassed for STFL.

STFL is a privileged instruction and using LowCore requires
!CONFIG_USER_ONLY, so add the ifdef and move the declaration to the
right place.

This was originally part of a bigger STFL(E) refactoring.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>


The other two patches, I will resend once we know how to handle the TLB
invalidation.

>>
>> Based on: https://github.com/cohuck/qemu.git s390-next
>> Available on: https://github.com/dhildenb/qemu.git s390x_lap
>>
>>
>> David Hildenbrand (3):
>>   accel/tcg: allow to invalidate a write TLB entry immediately
>>   s390x/tcg: low-address protection support
>>   s390x/tcg: make STFL store into the lowcore
>>
>>  accel/tcg/cputlb.c           |  5 ++-
>>  accel/tcg/softmmu_template.h |  4 +-
>>  include/exec/cpu-all.h       |  3 ++
>>  target/s390x/excp_helper.c   |  3 +-
>>  target/s390x/helper.h        |  2 +-
>>  target/s390x/mem_helper.c    |  8 ----
>>  target/s390x/misc_helper.c   |  7 +++-
>>  target/s390x/mmu_helper.c    | 96 ++++++++++++++++++++++++++++----------------
>>  8 files changed, 78 insertions(+), 50 deletions(-)
>>
> 


-- 

Thanks,

David